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Microsoft Exchange Server Remote Code Execution Vulnerability

cve CVE-2021-26858 3 sources, 3 claims · Watch

CISA Known Exploited Vulnerabilities writes:
Microsoft Exchange Server Remote Code Execution Vulnerability Microsoft Exchange Server contains an unspecified vulnerability that allows for remote code execution. This vulnerability is part of the ProxyLogon exploit chain. Apply updates per vendor instructions. Reference CISA's ED 21-02 (https://www.cisa.gov/news-events/directives/ed-21-02-mitigate-microsoft-exchange-premises-product-vulnerabilities) for further guidance and requirements. Note: The due date for addressing this vulnerability aligns with the requirements outlined in ED 21-02. https://nvd.nist.gov/vuln/detail/CVE-2021-26858 the claim
Severity
HIGH NVD
CVSS
7.8 NVD
EPSS
0.93651 EPSS
Exploited
yes CISA Known Exploited Vulnerabilities
Known ransomware campaign use
Known CISA Known Exploited Vulnerabilities
Due date
2022-05-03 CISA Known Exploited Vulnerabilities
Fixed in
15.00.1395.012, 15.00.1473.006, 15.00.1497.012, 15.01.1531.012, 15.01.1591.018, 15.01.1713.010, 15.01.1779.008, 15.01.1847.012, 15.01.1913.012, 15.01.1979.008, 15.01.2044.013, 15.01.2106.013, 15.01.2176.009, 15.01.1415.010, 15.01.1466.016, 15.02.0221.018, 15.01.1979.006, 15.02.0397.011, 15.02.0464.015, 15.02.0659.012, 15.02.0595.008, 15.02.0529.013, 15.02.0721.013, 15.02.0792.010 NVD
Vendor
Microsoft CISA Known Exploited Vulnerabilities
Microsoft NVD
Product
Exchange Server CISA Known Exploited Vulnerabilities
Microsoft Exchange Server 2013 Cumulative Update 21 NVD

How far exploitation has got

  1. No public code known
  2. Proof of concept
  3. Proof of concept, verified
  4. A Metasploit module
  5. Exploited in the wild · CISA Known Exploited Vulnerabilities 2021-11-03
  6. Used in ransomware campaigns · CISA Known Exploited Vulnerabilities 2021-11-03

Timeline

2021-03-03first spoke of it: Microsoft Exchange Server Remote Code Execution VulnerabilityNVD
2021-11-03first spoke of it: Microsoft Exchange Server Remote Code Execution VulnerabilityCISA Known Exploited Vulnerabilities
2022-05-03Due dateCISA Known Exploited Vulnerabilities
2026-10-05first spoke of it: CVE-2021-26858EPSS

What it is to other things

affectsmicrosoft/exchange_server
NVD
made_bymicrosoft
NVD

In words only, so not counted until a person confirms one:

affectsmicrosoft/microsoft_exchange_server_2013_cumulative_update_21
NVD says “Microsoft · Microsoft Exchange Server 2013 Cumulative Update 21”
Every value, with what each source said and its receipt
PropertySourceSaidMeans here
Automatable
automatable
NVDyes
An attacker can reliably run all of the kill chain's first four steps without a person.
receipt
Source
NVD
Its words
yes
Read by
field:cve.metrics.ssvcV203[].ssvcData.options[].automatable
Said since
2026-10-06 11:54 UTC
Last answered
2026-10-06 12:41 UTC
Original
open at the source
2026-10-06 11:54 UTCyes
2026-10-02 12:00 UTC—
What the source handed over
{
  "cve": {
    "affected": [
      {
        "affectedData": [
          {
            "platforms": [
              "x64-based Systems"
            ],
            "product": "Microsoft Exchange Server 2013 Cumulative Update 21",
            "vendor": "Microsoft",
            "versions": [
              {
                "lessThan": "15.00.1395.012",
                "status": "affected",
                "version": "15.00.0",
                "versionType": "custom"
              }
            ]
          },
          {
            "platforms": [
              "x64-based Systems"
            ],
            "product": "Microsoft Exchange Server 2013 Cumulative Update 22",
            "vendor": "Microsoft",
            "versions": [
              {
                "lessThan": "15.00.1473.006",
                "status": "affected",
                "version": "15.00.0",
                "versionType": "custom"
              }
            ]
          },
          {
            "platforms": [
              "x64-based Systems"
            ],
            "product": "Microsoft Exchange Server 2013 Cumulative Update 23",
            "vendor": "Microsoft",
            "versions": [
              {
                "lessThan": "15.00.1497.012",
                "status": "affected",
                "version": "15.00.0",
                "versionType": "custom"
              }
            ]
          },
          {
            "platforms": [
              "x64-based Systems"
            ],
            "product": "Microsoft Exchange Server 2016 Cumulative Update 10",
            "vendor": "Microsoft",
            "versions": [
              {
                "lessThan": "15.01.1531.012",
                "status": "affected",
                "version": "15.01.0",
                "versionType": "custom"
              }
            ]
          },
          {
            "platforms": [
              "x64-based Systems"
            ],
            "product": "Microsoft Exchange Server 2016 Cumulative Update 11",
            "vendor": "Microsoft",
            "versions": [
              {
                "lessThan": "15.01.1591.018",
                "status": "affected",
                "version": "15.01.0",
                "versionType": "custom"
              }
            ]
          },
          {
            "platforms": [
              "x64-based Systems"
            ],
            "product": "Microsoft Exchange Server 2016 Cumulative Update 12",
            "vendor": "Microsoft",
            "versions": [
              {
                "lessThan": "15.01.1713.010",
                "status": "affected",
                "version": "15.01.0",
                "versionType": "custom"
              }
            ]
          },
          {
            "platforms": [
              "x64-based Systems"
            ],
            "product": "Microsoft Exchange Server 2016 Cumulative Update 13",
            "vendor": "Microsoft",
            "versions": [
              {
                "lessThan": "15.01.1779.008",
                "status": "affected",
                "version": "15.01.0",
                "versionType": "custom"
              }
            ]
          },
          {
            "platforms": [
              "x64-based Systems"
            ],
            "product": "Microsoft Exchange Server 2016 Cumulative Update 14",
            "vendor": "Microsoft",
            "versions": [
              {
                "lessThan": "15.01.1847.012",
                "status": "affected",
                "version": "15.01.0",
                "versionType": "custom"
              }
            ]
          },
          {
            "platforms": [
              "x64-based Systems"
            ],
            "product": "Microsoft Exchange Server 2016 Cumulative Update 15",
            "vendor": "Microsoft",
            "versions": [
              {
                "lessThan": "15.01.1913.012",
                "status": "affected",
                "version": "15.01.0",
                "versionType": "custom"
              }
            ]
          },
          {
            "platforms": [
              "x64-based Systems"
            ],
            "product": "Microsoft Exchange Server 2016 Cumulative Update 16",
            "vendor": "Microsoft",
            "versions": [
              {
                "lessThan": "15.01.1979.008",
                "status": "affected",
                "version": "15.01.0",
                "versionType": "custom"
              }
            ]
          },
          {
            "platforms": [
              "x64-based Systems"
            ],
            "product": "Microsoft Exchange Server 2016 Cumulative Update 17",
            "vendor": "Microsoft",
            "versions": [
              {
                "lessThan": "15.01.2044.013",
                "status": "affected",
                "version": "15.01.0",
                "versionType": "custom"
              }
            ]
          },
          {
            "platforms": [
              "x64-based Systems"
            ],
            "product": "Microsoft Exchange Server 2016 Cumulative Update 18",
            "vendor": "Microsoft",
            "versions": [
              {
                "lessThan": "15.01.2106.013",
                "status": "affected",
                "version": "15.01.0",
                "versionType": "custom"
              }
            ]
          },
          {
            "platforms": [
              "x64-based Systems"
            ],
            "product": "Microsoft Exchange Server 2016 Cumulative Update 19",
            "vendor": "Microsoft",
            "versions": [
              {
                "lessThan": "15.01.2176.009",
                "status": "affected",
                "version": "15.01.0",
                "versionType": "custom"
              }
            ]
          },
          {
            "platforms": [
              "x64-based Systems"
            ],
            "product": "Microsoft Exchange Server 2016 Cumulative Update 8",
            "vendor": "Microsoft",
            "versions": [
              {
                "lessThan": "15.01.1415.010",
                "status": "affected",
                "version": "15.01.0",
                "versionType": "custom"
              }
            ]
          },
          {
            "platforms": [
              "x64-based Systems"
            ],
            "product": "Microsoft Exchange Server 2016 Cumulative Update 9",
            "vendor": "Microsoft",
            "versions": [
              {
                "lessThan": "15.01.1466.016",
                "status": "affected",
                "version": "15.01.0",
                "versionType": "custom"
              }
            ]
          },
          {
            "platforms": [
              "x64-based Systems"
            ],
            "product": "Microsoft Exchange Server 2019",
            "vendor": "Microsoft",
            "versions": [
              {
                "lessThan": "15.02.0221.018",
                "status": "affected",
                "version": "15.02.0",
                "versionType": "custom"
              }
            ]
          },
          {
            "platforms": [
              "x64-based Systems"
            ],
            "product": "Microsoft Exchange Server 2019 Cumulative Update 1",
            "vendor": "Microsoft",
            "versions": [
              {
                "lessThan": "15.01.1979.006",
                "status": "affected",
                "version": "15.02.0",
                "versionType": "custom"
              }
            ]
          },
          {
            "platforms": [
              "x64-based Systems"
            ],
            "product": "Microsoft Exchange Server 2019 Cumulative Update 2",
            "vendor": "Microsoft",
            "versions": [
              {
                "lessThan": "15.02.0397.011",
                "status": "affected",
                "version": "15.02.0",
                "versionType": "custom"
              }
            ]
          },
          {
            "platforms": [
              "x64-based Systems"
            ],
            "product": "Microsoft Exchange Server 2019 Cumulative Update 3",
            "vendor": "Microsoft",
            "versions": [
              {
                "lessThan": "15.02.0464.015",
                "status": "affected",
                "version": "15.02.0",
                "versionType": "custom"
              }
            ]
          },
          {
            "platforms": [
              "x64-based Systems"
            ],
            "product": "Microsoft Exchange Server 2019 Cumulative Update 4",
            "vendor": "Microsoft",
            "versions": [
              {
                "lessThan": "15.02.0659.012",
                "status": "affected",
                "version": "15.02.0",
                "versionType": "custom"
              }
            ]
          },
          {
            "platforms": [
              "x64-based Systems"
            ],
            "product": "Microsoft Exchange Server 2019 Cumulative Update 5",
            "vendor": "Microsoft",
            "versions": [
              {
                "lessThan": "15.02.0595.008",
                "status": "affected",
                "version": "15.02.0",
                "versionType": "custom"
              }
            ]
          },
          {
            "platforms": [
              "x64-based Systems"
            ],
            "product": "Microsoft Exchange Server 2019 Cumulative Update 6",
            "vendor": "Microsoft",
            "versions": [
              {
                "lessThan": "15.02.0529.013",
                "status": "affected",
                "version": "15.02.0",
                "versionType": "custom"
              }
            ]
          },
          {
            "platforms": [
              "x64-based Systems"
            ],
            "product": "Microsoft Exchange Server 2019 Cumulative Update 7",
            "vendor": "Microsoft",
            "versions": [
              {
                "lessThan": "15.02.0721.013",
                "status": "affected",
                "version": "15.02.0",
                "versionType": "custom"
              }
            ]
          },
          {
            "platforms": [
              "x64-based Systems"
            ],
            "product": "Microsoft Exchange Server 2019 Cumulative Update 8",
            "vendor": "Microsoft",
            "versions": [
              {
                "lessThan": "15.02.0792.010",
                "status": "affected",
                "version": "15.02.0",
                "versionType": "custom"
              }
            ]
          }
        ],
        "source": "secure@microsoft.com"
      }
    ],
    "cisaActionDue": "2022-05-03",
    "cisaExploitAdd": "2021-11-03",
    "cisaRequiredAction": "Apply updates per vendor instructions.",
    "cisaVulnerabilityName": "Microsoft Exchange Server Remote Code Execution Vulnerability",
    "configurations": [
      {
        "nodes": [
          {
            "cpeMatch": [
              {
                "criteria": "cpe:2.3:a:microsoft:exchange_server:2013:cumulative_update_21:*:*:*:*:*:*",
                "matchCriteriaId": "B560F8FD-068E-4A16-A37F-A62DCE88FCF2",
                "vulnerable": true
              },
              {
                "criteria": "cpe:2.3:a:microsoft:exchange_server:2013:cumulative_update_22:*:*:*:*:*:*",
                "matchCriteriaId": "751FD35F-2ECD-4B75-9589-988CC6AD3058",
                "vulnerable": true
              },
              {
                "criteria": "cpe:2.3:a:microsoft:exchange_server:2013:cumulative_update_23:*:*:*:*:*:*",
                "matchCriteriaId": "DA166F2A-D83B-4D50-AD0B-668D813E0585",
                "vulnerable": true
              },
              {
                "criteria": "cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_10:*:*:*:*:*:*",
                "matchCriteriaId": "63E362CB-CF75-4B7E-A4B1-D6D84AFCBB68",
                "vulnerable": true
              },
              {
                "criteria": "cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_11:*:*:*:*:*:*",
                "matchCriteriaId": "9BE04790-85A2-4078-88CE-1787BC5172E7",
                "vulnerable": true
              },
              {
                "criteria": "cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_12:*:*:*:*:*:*",
                "matchCriteriaId": "CCF101BE-27FD-4E2D-A694-C606BD3D1ED7",
                "vulnerable": true
              },
              {
                "criteria": "cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_13:*:*:*:*:*:*",
                "matchCriteriaId": "4DF5BDB5-205D-4B64-A49A-0152AFCF4A13",
                "vulnerable": true
              },
              {
                "criteria": "cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_14:*:*:*:*:*:*",
                "matchCriteriaId": "55284CF7-0D04-4216-83FE-4B1F9CA94207",
                "vulnerable": true
              },
              {
                "criteria": "cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_15:*:*:*:*:*:*",
                "matchCriteriaId": "CA2CE223-AA49-49E6-AC32-59270EFF55AD",
                "vulnerable": true
              },
              {
                "criteria": "cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_16:*:*:*:*:*:*",
                "matchCriteriaId": "4830D6A9-AF74-480C-8F69-8648CD619980",
                "vulnerable": true
              },
              {
                "criteria": "cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_17:*:*:*:*:*:*",
                "matchCriteriaId": "079E1E3F-FF25-4B0D-AC98-191D6455A014",
                "vulnerable": true
              },
              {
                "criteria": "cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_18:*:*:*:*:*:*",
                "matchCriteriaId": "29805EC7-6403-44B9-91EC-109C087E98EB",
                "vulnerable": true
              },
              {
                "criteria": "cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_19:*:*:*:*:*:*",
                "matchCriteriaId": "28FCA0E8-7D27-4746-9731-91B834CA3E64",
                "vulnerable": true
              },
              {
                "criteria": "cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_8:*:*:*:*:*:*",
                "matchCriteriaId": "075E907F-AF2F-4C31-86C7-51972BE412A1",
                "vulnerable": true
              },
              {
                "criteria": "cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_9:*:*:*:*:*:*",
                "matchCriteriaId": "69AF19DC-3D65-49A8-A85F-511085CDF27B",
                "vulnerable": true
              },
              {
                "criteria": "cpe:2.3:a:microsoft:exchange_server:2019:-:*:*:*:*:*:*",
                "matchCriteriaId": "40D8A6DB-9225-4A3F-AD76-192F6CCCF002",
                "vulnerable": true
              },
              {
                "criteria": "cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_1:*:*:*:*:*:*",
                "matchCriteriaId": "051DE6C4-7456-4C42-BC51-253208AADB4E",
                "vulnerable": true
              },
              {
                "criteria": "cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_2:*:*:*:*:*:*",
                "matchCriteriaId": "EE320413-D2C9-4B28-89BF-361B44A3F0FF",
                "vulnerable": true
              },
              {
                "criteria": "cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_3:*:*:*:*:*:*",
                "matchCriteriaId": "104F96DC-E280-4E0A-8586-B043B55888C2",
                "vulnerable": true
              },
              {
                "criteria": "cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_4:*:*:*:*:*:*",
                "matchCriteriaId": "73B3B3FE-7E85-4B86-A983-2C410FFEF4B8",
                "vulnerable": true
              },
              {
                "criteria": "cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_5:*:*:*:*:*:*",
                "matchCriteriaId": "8A9FB275-7F17-48B2-B528-BE89309D2AF5",
                "vulnerable": true
              },
              {
                "criteria": "cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_6:*:*:*:*:*:*",
                "matchCriteriaId": "D4AB3C25-CEA8-4D66-AEE4-953C8B17911A",
                "vulnerable": true
              },
              {
                "criteria": "cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_7:*:*:*:*:*:*",
                "matchCriteriaId": "36CE5C6D-9A04-41F5-AE7C-265779833649",
                "vulnerable": true
              },
              {
                "criteria": "cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_8:*:*:*:*:*:*",
                "matchCriteriaId": "44ECF39A-1DE1-4870-A494-06A53494338D",
                "vulnerable": true
              }
            ],
            "negate": false,
            "operator": "OR"
          }
        ]
      }
    ],
    "cveTags": [],
    "descriptions": [
      {
        "lang": "en",
        "value": "Microsoft Exchange Server Remote Code Execution Vulnerability"
      },
      {
        "lang": "es",
        "value": "Una Vulnerabilidad de Ejecución de código remota de Microsoft Exchange Server. Este ID de CVE es diferente de CVE-2021-26412, CVE-2021-26854, CVE-2021-26855, CVE-2021-26857, CVE-2021-27065, CVE-2021-27078"
      }
    ],
    "id": "CVE-2021-26858",
    "lastModified": "2026-10-01T21:17:16.777",
    "metrics": {
      "cvssMetricV2": [
        {
          "acInsufInfo": false,
          "baseSeverity": "MEDIUM",
          "cvssData": {
            "accessComplexity": "MEDIUM",
            "accessVector": "NETWORK",
            "authentication": "NONE",
            "availabilityImpact": "PARTIAL",
            "baseScore": 6.8,
            "confidentialityImpact": "PARTIAL",
            "integrityImpact": "PARTIAL",
            "vectorString": "AV:N/AC:M/Au:N/C:P/I:P/A:P",
            "version": "2.0"
          },
          "exploitabilityScore": 8.6,
          "impactScore": 6.4,
          "obtainAllPrivilege": false,
          "obtainOtherPrivilege": false,
          "obtainUserPrivilege": false,
          "source": "nvd@nist.gov",
          "type": "Primary",
          "userInteractionRequired": true
        }
      ],
      "cvssMetricV31": [
        {
          "cvssData": {
            "attackComplexity": "LOW",
            "attackVector": "LOCAL",
            "availabilityImpact": "HIGH",
            "baseScore": 7.8,
            "baseSeverity": "HIGH",
            "confidentialityImpact": "HIGH",
            "integrityImpact": "HIGH",
            "privilegesRequired": "NONE",
            "scope": "UNCHANGED",
            "userInteraction": "REQUIRED",
            "vectorString": "CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H",
            "version": "3.1"
          },
          "exploitabilityScore": 1.8,
          "impactScore": 5.9,
          "source": "secure@microsoft.com",
          "type": "Secondary"
        },
        {
          "cvssData": {
            "attackComplexity": "LOW",
            "attackVector": "LOCAL",
            "availabilityImpact": "HIGH",
            "baseScore": 7.8,
            "baseSeverity": "HIGH",
            "confidentialityImpact": "HIGH",
            "integrityImpact": "HIGH",
            "privilegesRequired": "NONE",
            "scope": "UNCHANGED",
            "userInteraction": "REQUIRED",
            "vectorString": "CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H",
            "version": "3.1"
          },
          "exploitabilityScore": 1.8,
          "impactScore": 5.9,
          "source": "nvd@nist.gov",
          "type": "Secondary"
        }
      ],
      "ssvcV203": [
        {
          "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "ssvcData": {
            "id": "CVE-2021-26858",
            "options": [
              {
                "exploitation": "active"
              },
              {
                "automatable": "yes"
              },
              {
                "technicalImpact": "total"
              }
            ],
            "role": "CISA Coordinator",
            "timestamp": "2026-08-12T03:55:36.937537Z",
            "version": "2.0.3"
          }
        }
      ]
    },
    "published": "2021-03-03T00:15:12.227",
    "references": [
      {
        "source": "secure@microsoft.com",
        "tags": [
          "Patch",
          "Vendor Advisory"
        ],
        "url": "https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-26858"
      },
      {
        "source": "af854a3a-2127-422b-91ae-364da2661108",
        "tags": [
          "Patch",
          "Vendor Advisory"
        ],
        "url": "https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-26858"
      },
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "tags": [
          "US Government Resource"
        ],
        "url": "https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-26858"
      }
    ],
    "sourceIdentifier": "secure@microsoft.com",
    "vulnStatus": "Analyzed",
    "weaknesses": [
      {
        "description": [
          {
            "lang": "en",
            "value": "NVD-CWE-noinfo"
          }
        ],
        "source": "nvd@nist.gov",
        "type": "Primary"
      }
    ]
  }
}
—
CVSS
cvss
NVD7.8
receipt
Source
NVD
Its words
7.8
Read by
field:cve.metrics.cvssMetricV31[type=Primary].cvssData.baseScore || field:cve.metrics.cvssMetricV31[].cvssData.baseScore
Said since
2026-10-02 12:00 UTC
Last answered
2026-10-06 12:41 UTC
Original
open at the source
What the source handed over
{
  "cve": {
    "affected": [
      {
        "affectedData": [
          {
            "platforms": [
              "x64-based Systems"
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    ],
    "cisaActionDue": "2022-05-03",
    "cisaExploitAdd": "2021-11-03",
    "cisaRequiredAction": "Apply updates per vendor instructions.",
    "cisaVulnerabilityName": "Microsoft Exchange Server Remote Code Execution Vulnerability",
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    "cveTags": [],
    "descriptions": [
      {
        "lang": "en",
        "value": "Microsoft Exchange Server Remote Code Execution Vulnerability"
      },
      {
        "lang": "es",
        "value": "Una Vulnerabilidad de Ejecución de código remota de Microsoft Exchange Server. Este ID de CVE es diferente de CVE-2021-26412, CVE-2021-26854, CVE-2021-26855, CVE-2021-26857, CVE-2021-27065, CVE-2021-27078"
      }
    ],
    "id": "CVE-2021-26858",
    "lastModified": "2026-10-01T21:17:16.777",
    "metrics": {
      "cvssMetricV2": [
        {
          "acInsufInfo": false,
          "baseSeverity": "MEDIUM",
          "cvssData": {
            "accessComplexity": "MEDIUM",
            "accessVector": "NETWORK",
            "authentication": "NONE",
            "availabilityImpact": "PARTIAL",
            "baseScore": 6.8,
            "confidentialityImpact": "PARTIAL",
            "integrityImpact": "PARTIAL",
            "vectorString": "AV:N/AC:M/Au:N/C:P/I:P/A:P",
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            "confidentialityImpact": "HIGH",
            "integrityImpact": "HIGH",
            "privilegesRequired": "NONE",
            "scope": "UNCHANGED",
            "userInteraction": "REQUIRED",
            "vectorString": "CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H",
            "version": "3.1"
          },
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          "type": "Secondary"
        },
        {
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            "privilegesRequired": "NONE",
            "scope": "UNCHANGED",
            "userInteraction": "REQUIRED",
            "vectorString": "CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H",
            "version": "3.1"
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          "type": "Secondary"
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      ],
      "ssvcV203": [
        {
          "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "ssvcData": {
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            "options": [
              {
                "exploitation": "active"
              },
              {
                "automatable": "yes"
              },
              {
                "technicalImpact": "total"
              }
            ],
            "role": "CISA Coordinator",
            "timestamp": "2026-08-12T03:55:36.937537Z",
            "version": "2.0.3"
          }
        }
      ]
    },
    "published": "2021-03-03T00:15:12.227",
    "references": [
      {
        "source": "secure@microsoft.com",
        "tags": [
          "Patch",
          "Vendor Advisory"
        ],
        "url": "https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-26858"
      },
      {
        "source": "af854a3a-2127-422b-91ae-364da2661108",
        "tags": [
          "Patch",
          "Vendor Advisory"
        ],
        "url": "https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-26858"
      },
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "tags": [
          "US Government Resource"
        ],
        "url": "https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-26858"
      }
    ],
    "sourceIdentifier": "secure@microsoft.com",
    "vulnStatus": "Analyzed",
    "weaknesses": [
      {
        "description": [
          {
            "lang": "en",
            "value": "NVD-CWE-noinfo"
          }
        ],
        "source": "nvd@nist.gov",
        "type": "Primary"
      }
    ]
  }
}
—
CVSS vector
cvss_vector
NVDCVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
receipt
Source
NVD
Its words
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
Read by
field:cve.metrics.cvssMetricV31[type=Primary].cvssData.vectorString || field:cve.metrics.cvssMetricV31[].cvssData.vectorString
Said since
2026-10-06 11:54 UTC
Last answered
2026-10-06 12:41 UTC
Original
open at the source
2026-10-06 11:54 UTCCVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
2026-10-02 12:00 UTC—
What the source handed over
{
  "cve": {
    "affected": [
      {
        "affectedData": [
          {
            "platforms": [
              "x64-based Systems"
            ],
            "product": "Microsoft Exchange Server 2013 Cumulative Update 21",
            "vendor": "Microsoft",
            "versions": [
              {
                "lessThan": "15.00.1395.012",
                "status": "affected",
                "version": "15.00.0",
                "versionType": "custom"
              }
            ]
          },
          {
            "platforms": [
              "x64-based Systems"
            ],
            "product": "Microsoft Exchange Server 2013 Cumulative Update 22",
            "vendor": "Microsoft",
            "versions": [
              {
                "lessThan": "15.00.1473.006",
                "status": "affected",
                "version": "15.00.0",
                "versionType": "custom"
              }
            ]
          },
          {
            "platforms": [
              "x64-based Systems"
            ],
            "product": "Microsoft Exchange Server 2013 Cumulative Update 23",
            "vendor": "Microsoft",
            "versions": [
              {
                "lessThan": "15.00.1497.012",
                "status": "affected",
                "version": "15.00.0",
                "versionType": "custom"
              }
            ]
          },
          {
            "platforms": [
              "x64-based Systems"
            ],
            "product": "Microsoft Exchange Server 2016 Cumulative Update 10",
            "vendor": "Microsoft",
            "versions": [
              {
                "lessThan": "15.01.1531.012",
                "status": "affected",
                "version": "15.01.0",
                "versionType": "custom"
              }
            ]
          },
          {
            "platforms": [
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            ],
            "product": "Microsoft Exchange Server 2016 Cumulative Update 11",
            "vendor": "Microsoft",
            "versions": [
              {
                "lessThan": "15.01.1591.018",
                "status": "affected",
                "version": "15.01.0",
                "versionType": "custom"
              }
            ]
          },
          {
            "platforms": [
              "x64-based Systems"
            ],
            "product": "Microsoft Exchange Server 2016 Cumulative Update 12",
            "vendor": "Microsoft",
            "versions": [
              {
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                "status": "affected",
                "version": "15.01.0",
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              }
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          },
          {
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            "product": "Microsoft Exchange Server 2016 Cumulative Update 13",
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          },
          {
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            ],
            "product": "Microsoft Exchange Server 2016 Cumulative Update 14",
            "vendor": "Microsoft",
            "versions": [
              {
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            ]
          },
          {
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            "product": "Microsoft Exchange Server 2019 Cumulative Update 5",
            "vendor": "Microsoft",
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            ]
          },
          {
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            ],
            "product": "Microsoft Exchange Server 2019 Cumulative Update 6",
            "vendor": "Microsoft",
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              }
            ]
          },
          {
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            "product": "Microsoft Exchange Server 2019 Cumulative Update 7",
            "vendor": "Microsoft",
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              {
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            ]
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          {
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            ]
          }
        ],
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      }
    ],
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    "cisaExploitAdd": "2021-11-03",
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            "negate": false,
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    ],
    "cveTags": [],
    "descriptions": [
      {
        "lang": "en",
        "value": "Microsoft Exchange Server Remote Code Execution Vulnerability"
      },
      {
        "lang": "es",
        "value": "Una Vulnerabilidad de Ejecución de código remota de Microsoft Exchange Server. Este ID de CVE es diferente de CVE-2021-26412, CVE-2021-26854, CVE-2021-26855, CVE-2021-26857, CVE-2021-27065, CVE-2021-27078"
      }
    ],
    "id": "CVE-2021-26858",
    "lastModified": "2026-10-01T21:17:16.777",
    "metrics": {
      "cvssMetricV2": [
        {
          "acInsufInfo": false,
          "baseSeverity": "MEDIUM",
          "cvssData": {
            "accessComplexity": "MEDIUM",
            "accessVector": "NETWORK",
            "authentication": "NONE",
            "availabilityImpact": "PARTIAL",
            "baseScore": 6.8,
            "confidentialityImpact": "PARTIAL",
            "integrityImpact": "PARTIAL",
            "vectorString": "AV:N/AC:M/Au:N/C:P/I:P/A:P",
            "version": "2.0"
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          "impactScore": 6.4,
          "obtainAllPrivilege": false,
          "obtainOtherPrivilege": false,
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          "source": "nvd@nist.gov",
          "type": "Primary",
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            "confidentialityImpact": "HIGH",
            "integrityImpact": "HIGH",
            "privilegesRequired": "NONE",
            "scope": "UNCHANGED",
            "userInteraction": "REQUIRED",
            "vectorString": "CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H",
            "version": "3.1"
          },
          "exploitabilityScore": 1.8,
          "impactScore": 5.9,
          "source": "secure@microsoft.com",
          "type": "Secondary"
        },
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            "privilegesRequired": "NONE",
            "scope": "UNCHANGED",
            "userInteraction": "REQUIRED",
            "vectorString": "CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H",
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      "ssvcV203": [
        {
          "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "ssvcData": {
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            "options": [
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                "exploitation": "active"
              },
              {
                "automatable": "yes"
              },
              {
                "technicalImpact": "total"
              }
            ],
            "role": "CISA Coordinator",
            "timestamp": "2026-08-12T03:55:36.937537Z",
            "version": "2.0.3"
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    "published": "2021-03-03T00:15:12.227",
    "references": [
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        "source": "secure@microsoft.com",
        "tags": [
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          "Vendor Advisory"
        ],
        "url": "https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-26858"
      },
      {
        "source": "af854a3a-2127-422b-91ae-364da2661108",
        "tags": [
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        "url": "https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-26858"
      },
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "tags": [
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        ],
        "url": "https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-26858"
      }
    ],
    "sourceIdentifier": "secure@microsoft.com",
    "vulnStatus": "Analyzed",
    "weaknesses": [
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            "value": "NVD-CWE-noinfo"
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        "source": "nvd@nist.gov",
        "type": "Primary"
      }
    ]
  }
}
—
Due date
due_date
CISA Known Exploited Vulnerabilities2022-05-03
receipt
Source
CISA Known Exploited Vulnerabilities
Its words
2022-05-03
Read by
field:dueDate
Said since
2026-09-28 11:44 UTC
Last answered
2026-10-06 17:36 UTC
What the source handed over
{
  "cveID": "CVE-2021-26858",
  "cwes": "",
  "dateAdded": "2021-11-03",
  "dueDate": "2022-05-03",
  "forensicTriage": "No",
  "knownRansomwareCampaignUse": "Known",
  "notes": "Reference CISA's ED 21-02 (https://www.cisa.gov/news-events/directives/ed-21-02-mitigate-microsoft-exchange-premises-product-vulnerabilities) for further guidance and requirements. Note: The due date for addressing this vulnerability aligns with the requirements outlined in ED 21-02. https://nvd.nist.gov/vuln/detail/CVE-2021-26858",
  "product": "Exchange Server",
  "requiredAction": "Apply updates per vendor instructions.",
  "shortDescription": "Microsoft Exchange Server contains an unspecified vulnerability that allows for remote code execution. This vulnerability is part of the ProxyLogon exploit chain.",
  "vendorProject": "Microsoft",
  "vulnerabilityName": "Microsoft Exchange Server Remote Code Execution Vulnerability"
}
—
EPSS
epss
EPSS0.93651
receipt
Source
EPSS
Its words
0.936510000
Read by
field:epss
Said since
2026-10-06 12:18 UTC
Last answered
2026-10-06 12:19 UTC
Original
open at the source
What the source handed over
{
  "cve": "CVE-2021-26858",
  "date": "2026-10-05",
  "epss": "0.936510000",
  "percentile": "0.998420000"
}
—
EPSS percentile
epss_percentile
EPSS0.99842
receipt
Source
EPSS
Its words
0.998420000
Read by
field:percentile
Said since
2026-10-06 12:18 UTC
Last answered
2026-10-06 12:19 UTC
Original
open at the source
What the source handed over
{
  "cve": "CVE-2021-26858",
  "date": "2026-10-05",
  "epss": "0.936510000",
  "percentile": "0.998420000"
}
—
Exploitation
exploitation
NVDactive
Reliable evidence that it is exploited in the wild.
receipt
Source
NVD
Its words
active
Read by
field:cve.metrics.ssvcV203[].ssvcData.options[].exploitation
Said since
2026-10-06 11:54 UTC
Last answered
2026-10-06 12:41 UTC
Original
open at the source
2026-10-06 11:54 UTCactive
2026-10-02 12:00 UTC—
What the source handed over
{
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      {
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          {
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            ],
            "product": "Microsoft Exchange Server 2013 Cumulative Update 21",
            "vendor": "Microsoft",
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                "status": "affected",
                "version": "15.00.0",
                "versionType": "custom"
              }
            ]
          },
          {
            "platforms": [
              "x64-based Systems"
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            "product": "Microsoft Exchange Server 2013 Cumulative Update 22",
            "vendor": "Microsoft",
            "versions": [
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                "status": "affected",
                "version": "15.00.0",
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          },
          {
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            "product": "Microsoft Exchange Server 2013 Cumulative Update 23",
            "vendor": "Microsoft",
            "versions": [
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                "status": "affected",
                "version": "15.00.0",
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            "product": "Microsoft Exchange Server 2016 Cumulative Update 10",
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          },
          {
            "platforms": [
              "x64-based Systems"
            ],
            "product": "Microsoft Exchange Server 2016 Cumulative Update 12",
            "vendor": "Microsoft",
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                "status": "affected",
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          },
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              "x64-based Systems"
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            "product": "Microsoft Exchange Server 2016 Cumulative Update 13",
            "vendor": "Microsoft",
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          },
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            "product": "Microsoft Exchange Server 2016 Cumulative Update 14",
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            "product": "Microsoft Exchange Server 2016 Cumulative Update 15",
            "vendor": "Microsoft",
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              "x64-based Systems"
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            "product": "Microsoft Exchange Server 2016 Cumulative Update 16",
            "vendor": "Microsoft",
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                "status": "affected",
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              }
            ]
          },
          {
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            ],
            "product": "Microsoft Exchange Server 2016 Cumulative Update 17",
            "vendor": "Microsoft",
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                "status": "affected",
                "version": "15.01.0",
                "versionType": "custom"
              }
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          {
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            ],
            "product": "Microsoft Exchange Server 2016 Cumulative Update 18",
            "vendor": "Microsoft",
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                "status": "affected",
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            ]
          },
          {
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            ],
            "product": "Microsoft Exchange Server 2016 Cumulative Update 19",
            "vendor": "Microsoft",
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                "status": "affected",
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          {
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            ],
            "product": "Microsoft Exchange Server 2016 Cumulative Update 8",
            "vendor": "Microsoft",
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              {
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                "status": "affected",
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                "versionType": "custom"
              }
            ]
          },
          {
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            ],
            "product": "Microsoft Exchange Server 2016 Cumulative Update 9",
            "vendor": "Microsoft",
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              {
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                "status": "affected",
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                "versionType": "custom"
              }
            ]
          },
          {
            "platforms": [
              "x64-based Systems"
            ],
            "product": "Microsoft Exchange Server 2019",
            "vendor": "Microsoft",
            "versions": [
              {
                "lessThan": "15.02.0221.018",
                "status": "affected",
                "version": "15.02.0",
                "versionType": "custom"
              }
            ]
          },
          {
            "platforms": [
              "x64-based Systems"
            ],
            "product": "Microsoft Exchange Server 2019 Cumulative Update 1",
            "vendor": "Microsoft",
            "versions": [
              {
                "lessThan": "15.01.1979.006",
                "status": "affected",
                "version": "15.02.0",
                "versionType": "custom"
              }
            ]
          },
          {
            "platforms": [
              "x64-based Systems"
            ],
            "product": "Microsoft Exchange Server 2019 Cumulative Update 2",
            "vendor": "Microsoft",
            "versions": [
              {
                "lessThan": "15.02.0397.011",
                "status": "affected",
                "version": "15.02.0",
                "versionType": "custom"
              }
            ]
          },
          {
            "platforms": [
              "x64-based Systems"
            ],
            "product": "Microsoft Exchange Server 2019 Cumulative Update 3",
            "vendor": "Microsoft",
            "versions": [
              {
                "lessThan": "15.02.0464.015",
                "status": "affected",
                "version": "15.02.0",
                "versionType": "custom"
              }
            ]
          },
          {
            "platforms": [
              "x64-based Systems"
            ],
            "product": "Microsoft Exchange Server 2019 Cumulative Update 4",
            "vendor": "Microsoft",
            "versions": [
              {
                "lessThan": "15.02.0659.012",
                "status": "affected",
                "version": "15.02.0",
                "versionType": "custom"
              }
            ]
          },
          {
            "platforms": [
              "x64-based Systems"
            ],
            "product": "Microsoft Exchange Server 2019 Cumulative Update 5",
            "vendor": "Microsoft",
            "versions": [
              {
                "lessThan": "15.02.0595.008",
                "status": "affected",
                "version": "15.02.0",
                "versionType": "custom"
              }
            ]
          },
          {
            "platforms": [
              "x64-based Systems"
            ],
            "product": "Microsoft Exchange Server 2019 Cumulative Update 6",
            "vendor": "Microsoft",
            "versions": [
              {
                "lessThan": "15.02.0529.013",
                "status": "affected",
                "version": "15.02.0",
                "versionType": "custom"
              }
            ]
          },
          {
            "platforms": [
              "x64-based Systems"
            ],
            "product": "Microsoft Exchange Server 2019 Cumulative Update 7",
            "vendor": "Microsoft",
            "versions": [
              {
                "lessThan": "15.02.0721.013",
                "status": "affected",
                "version": "15.02.0",
                "versionType": "custom"
              }
            ]
          },
          {
            "platforms": [
              "x64-based Systems"
            ],
            "product": "Microsoft Exchange Server 2019 Cumulative Update 8",
            "vendor": "Microsoft",
            "versions": [
              {
                "lessThan": "15.02.0792.010",
                "status": "affected",
                "version": "15.02.0",
                "versionType": "custom"
              }
            ]
          }
        ],
        "source": "secure@microsoft.com"
      }
    ],
    "cisaActionDue": "2022-05-03",
    "cisaExploitAdd": "2021-11-03",
    "cisaRequiredAction": "Apply updates per vendor instructions.",
    "cisaVulnerabilityName": "Microsoft Exchange Server Remote Code Execution Vulnerability",
    "configurations": [
      {
        "nodes": [
          {
            "cpeMatch": [
              {
                "criteria": "cpe:2.3:a:microsoft:exchange_server:2013:cumulative_update_21:*:*:*:*:*:*",
                "matchCriteriaId": "B560F8FD-068E-4A16-A37F-A62DCE88FCF2",
                "vulnerable": true
              },
              {
                "criteria": "cpe:2.3:a:microsoft:exchange_server:2013:cumulative_update_22:*:*:*:*:*:*",
                "matchCriteriaId": "751FD35F-2ECD-4B75-9589-988CC6AD3058",
                "vulnerable": true
              },
              {
                "criteria": "cpe:2.3:a:microsoft:exchange_server:2013:cumulative_update_23:*:*:*:*:*:*",
                "matchCriteriaId": "DA166F2A-D83B-4D50-AD0B-668D813E0585",
                "vulnerable": true
              },
              {
                "criteria": "cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_10:*:*:*:*:*:*",
                "matchCriteriaId": "63E362CB-CF75-4B7E-A4B1-D6D84AFCBB68",
                "vulnerable": true
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              {
                "criteria": "cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_11:*:*:*:*:*:*",
                "matchCriteriaId": "9BE04790-85A2-4078-88CE-1787BC5172E7",
                "vulnerable": true
              },
              {
                "criteria": "cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_12:*:*:*:*:*:*",
                "matchCriteriaId": "CCF101BE-27FD-4E2D-A694-C606BD3D1ED7",
                "vulnerable": true
              },
              {
                "criteria": "cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_13:*:*:*:*:*:*",
                "matchCriteriaId": "4DF5BDB5-205D-4B64-A49A-0152AFCF4A13",
                "vulnerable": true
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              {
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                "matchCriteriaId": "55284CF7-0D04-4216-83FE-4B1F9CA94207",
                "vulnerable": true
              },
              {
                "criteria": "cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_15:*:*:*:*:*:*",
                "matchCriteriaId": "CA2CE223-AA49-49E6-AC32-59270EFF55AD",
                "vulnerable": true
              },
              {
                "criteria": "cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_16:*:*:*:*:*:*",
                "matchCriteriaId": "4830D6A9-AF74-480C-8F69-8648CD619980",
                "vulnerable": true
              },
              {
                "criteria": "cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_17:*:*:*:*:*:*",
                "matchCriteriaId": "079E1E3F-FF25-4B0D-AC98-191D6455A014",
                "vulnerable": true
              },
              {
                "criteria": "cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_18:*:*:*:*:*:*",
                "matchCriteriaId": "29805EC7-6403-44B9-91EC-109C087E98EB",
                "vulnerable": true
              },
              {
                "criteria": "cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_19:*:*:*:*:*:*",
                "matchCriteriaId": "28FCA0E8-7D27-4746-9731-91B834CA3E64",
                "vulnerable": true
              },
              {
                "criteria": "cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_8:*:*:*:*:*:*",
                "matchCriteriaId": "075E907F-AF2F-4C31-86C7-51972BE412A1",
                "vulnerable": true
              },
              {
                "criteria": "cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_9:*:*:*:*:*:*",
                "matchCriteriaId": "69AF19DC-3D65-49A8-A85F-511085CDF27B",
                "vulnerable": true
              },
              {
                "criteria": "cpe:2.3:a:microsoft:exchange_server:2019:-:*:*:*:*:*:*",
                "matchCriteriaId": "40D8A6DB-9225-4A3F-AD76-192F6CCCF002",
                "vulnerable": true
              },
              {
                "criteria": "cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_1:*:*:*:*:*:*",
                "matchCriteriaId": "051DE6C4-7456-4C42-BC51-253208AADB4E",
                "vulnerable": true
              },
              {
                "criteria": "cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_2:*:*:*:*:*:*",
                "matchCriteriaId": "EE320413-D2C9-4B28-89BF-361B44A3F0FF",
                "vulnerable": true
              },
              {
                "criteria": "cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_3:*:*:*:*:*:*",
                "matchCriteriaId": "104F96DC-E280-4E0A-8586-B043B55888C2",
                "vulnerable": true
              },
              {
                "criteria": "cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_4:*:*:*:*:*:*",
                "matchCriteriaId": "73B3B3FE-7E85-4B86-A983-2C410FFEF4B8",
                "vulnerable": true
              },
              {
                "criteria": "cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_5:*:*:*:*:*:*",
                "matchCriteriaId": "8A9FB275-7F17-48B2-B528-BE89309D2AF5",
                "vulnerable": true
              },
              {
                "criteria": "cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_6:*:*:*:*:*:*",
                "matchCriteriaId": "D4AB3C25-CEA8-4D66-AEE4-953C8B17911A",
                "vulnerable": true
              },
              {
                "criteria": "cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_7:*:*:*:*:*:*",
                "matchCriteriaId": "36CE5C6D-9A04-41F5-AE7C-265779833649",
                "vulnerable": true
              },
              {
                "criteria": "cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_8:*:*:*:*:*:*",
                "matchCriteriaId": "44ECF39A-1DE1-4870-A494-06A53494338D",
                "vulnerable": true
              }
            ],
            "negate": false,
            "operator": "OR"
          }
        ]
      }
    ],
    "cveTags": [],
    "descriptions": [
      {
        "lang": "en",
        "value": "Microsoft Exchange Server Remote Code Execution Vulnerability"
      },
      {
        "lang": "es",
        "value": "Una Vulnerabilidad de Ejecución de código remota de Microsoft Exchange Server. Este ID de CVE es diferente de CVE-2021-26412, CVE-2021-26854, CVE-2021-26855, CVE-2021-26857, CVE-2021-27065, CVE-2021-27078"
      }
    ],
    "id": "CVE-2021-26858",
    "lastModified": "2026-10-01T21:17:16.777",
    "metrics": {
      "cvssMetricV2": [
        {
          "acInsufInfo": false,
          "baseSeverity": "MEDIUM",
          "cvssData": {
            "accessComplexity": "MEDIUM",
            "accessVector": "NETWORK",
            "authentication": "NONE",
            "availabilityImpact": "PARTIAL",
            "baseScore": 6.8,
            "confidentialityImpact": "PARTIAL",
            "integrityImpact": "PARTIAL",
            "vectorString": "AV:N/AC:M/Au:N/C:P/I:P/A:P",
            "version": "2.0"
          },
          "exploitabilityScore": 8.6,
          "impactScore": 6.4,
          "obtainAllPrivilege": false,
          "obtainOtherPrivilege": false,
          "obtainUserPrivilege": false,
          "source": "nvd@nist.gov",
          "type": "Primary",
          "userInteractionRequired": true
        }
      ],
      "cvssMetricV31": [
        {
          "cvssData": {
            "attackComplexity": "LOW",
            "attackVector": "LOCAL",
            "availabilityImpact": "HIGH",
            "baseScore": 7.8,
            "baseSeverity": "HIGH",
            "confidentialityImpact": "HIGH",
            "integrityImpact": "HIGH",
            "privilegesRequired": "NONE",
            "scope": "UNCHANGED",
            "userInteraction": "REQUIRED",
            "vectorString": "CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H",
            "version": "3.1"
          },
          "exploitabilityScore": 1.8,
          "impactScore": 5.9,
          "source": "secure@microsoft.com",
          "type": "Secondary"
        },
        {
          "cvssData": {
            "attackComplexity": "LOW",
            "attackVector": "LOCAL",
            "availabilityImpact": "HIGH",
            "baseScore": 7.8,
            "baseSeverity": "HIGH",
            "confidentialityImpact": "HIGH",
            "integrityImpact": "HIGH",
            "privilegesRequired": "NONE",
            "scope": "UNCHANGED",
            "userInteraction": "REQUIRED",
            "vectorString": "CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H",
            "version": "3.1"
          },
          "exploitabilityScore": 1.8,
          "impactScore": 5.9,
          "source": "nvd@nist.gov",
          "type": "Secondary"
        }
      ],
      "ssvcV203": [
        {
          "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "ssvcData": {
            "id": "CVE-2021-26858",
            "options": [
              {
                "exploitation": "active"
              },
              {
                "automatable": "yes"
              },
              {
                "technicalImpact": "total"
              }
            ],
            "role": "CISA Coordinator",
            "timestamp": "2026-08-12T03:55:36.937537Z",
            "version": "2.0.3"
          }
        }
      ]
    },
    "published": "2021-03-03T00:15:12.227",
    "references": [
      {
        "source": "secure@microsoft.com",
        "tags": [
          "Patch",
          "Vendor Advisory"
        ],
        "url": "https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-26858"
      },
      {
        "source": "af854a3a-2127-422b-91ae-364da2661108",
        "tags": [
          "Patch",
          "Vendor Advisory"
        ],
        "url": "https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-26858"
      },
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "tags": [
          "US Government Resource"
        ],
        "url": "https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-26858"
      }
    ],
    "sourceIdentifier": "secure@microsoft.com",
    "vulnStatus": "Analyzed",
    "weaknesses": [
      {
        "description": [
          {
            "lang": "en",
            "value": "NVD-CWE-noinfo"
          }
        ],
        "source": "nvd@nist.gov",
        "type": "Primary"
      }
    ]
  }
}
—
Exploited
exploited
CISA Known Exploited Vulnerabilitiesyes
receipt
Source
CISA Known Exploited Vulnerabilities
Its words
yes
Read by
const:yes
Said since
2026-09-28 11:44 UTC
Last answered
2026-10-06 17:36 UTC
What the source handed over
{
  "cveID": "CVE-2021-26858",
  "cwes": "",
  "dateAdded": "2021-11-03",
  "dueDate": "2022-05-03",
  "forensicTriage": "No",
  "knownRansomwareCampaignUse": "Known",
  "notes": "Reference CISA's ED 21-02 (https://www.cisa.gov/news-events/directives/ed-21-02-mitigate-microsoft-exchange-premises-product-vulnerabilities) for further guidance and requirements. Note: The due date for addressing this vulnerability aligns with the requirements outlined in ED 21-02. https://nvd.nist.gov/vuln/detail/CVE-2021-26858",
  "product": "Exchange Server",
  "requiredAction": "Apply updates per vendor instructions.",
  "shortDescription": "Microsoft Exchange Server contains an unspecified vulnerability that allows for remote code execution. This vulnerability is part of the ProxyLogon exploit chain.",
  "vendorProject": "Microsoft",
  "vulnerabilityName": "Microsoft Exchange Server Remote Code Execution Vulnerability"
}
—
Fixed in
fixed_in
NVD15.00.1395.012, 15.00.1473.006, 15.00.1497.012, 15.01.1531.012, 15.01.1591.018, 15.01.1713.010, 15.01.1779.008, 15.01.1847.012, 15.01.1913.012, 15.01.1979.008, 15.01.2044.013, 15.01.2106.013, 15.01.2176.009, 15.01.1415.010, 15.01.1466.016, 15.02.0221.018, 15.01.1979.006, 15.02.0397.011, 15.02.0464.015, 15.02.0659.012, 15.02.0595.008, 15.02.0529.013, 15.02.0721.013, 15.02.0792.010
receipt
Source
NVD
Its words
15.00.1395.012, 15.00.1473.006, 15.00.1497.012, 15.01.1531.012, 15.01.1591.018, 15.01.1713.010, 15.01.1779.008, 15.01.1847.012, 15.01.1913.012, 15.01.1979.008, 15.01.2044.013, 15.01.2106.013, 15.01.2176.009, 15.01.1415.010, 15.01.1466.016, 15.02.0221.018, 15.01.1979.006, 15.02.0397.011, 15.02.0464.015, 15.02.0659.012, 15.02.0595.008, 15.02.0529.013, 15.02.0721.013, 15.02.0792.010
Read by
field:cve.affected[].affectedData[].versions[status=affected].lessThan
Said since
2026-10-06 11:54 UTC
Last answered
2026-10-06 12:41 UTC
Original
open at the source
2026-10-06 11:54 UTC15.00.1395.012, 15.00.1473.006, 15.00.1497.012, 15.01.1531.012, 15.01.1591.018, 15.01.1713.010, 15.01.1779.008, 15.01.1847.012, 15.01.1913.012, 15.01.1979.008, 15.01.2044.013, 15.01.2106.013, 15.01.2176.009, 15.01.1415.010, 15.01.1466.016, 15.02.0221.018, 15.01.1979.006, 15.02.0397.011, 15.02.0464.015, 15.02.0659.012, 15.02.0595.008, 15.02.0529.013, 15.02.0721.013, 15.02.0792.010
2026-10-02 12:00 UTC—
What the source handed over
{
  "cve": {
    "affected": [
      {
        "affectedData": [
          {
            "platforms": [
              "x64-based Systems"
            ],
            "product": "Microsoft Exchange Server 2013 Cumulative Update 21",
            "vendor": "Microsoft",
            "versions": [
              {
                "lessThan": "15.00.1395.012",
                "status": "affected",
                "version": "15.00.0",
                "versionType": "custom"
              }
            ]
          },
          {
            "platforms": [
              "x64-based Systems"
            ],
            "product": "Microsoft Exchange Server 2013 Cumulative Update 22",
            "vendor": "Microsoft",
            "versions": [
              {
                "lessThan": "15.00.1473.006",
                "status": "affected",
                "version": "15.00.0",
                "versionType": "custom"
              }
            ]
          },
          {
            "platforms": [
              "x64-based Systems"
            ],
            "product": "Microsoft Exchange Server 2013 Cumulative Update 23",
            "vendor": "Microsoft",
            "versions": [
              {
                "lessThan": "15.00.1497.012",
                "status": "affected",
                "version": "15.00.0",
                "versionType": "custom"
              }
            ]
          },
          {
            "platforms": [
              "x64-based Systems"
            ],
            "product": "Microsoft Exchange Server 2016 Cumulative Update 10",
            "vendor": "Microsoft",
            "versions": [
              {
                "lessThan": "15.01.1531.012",
                "status": "affected",
                "version": "15.01.0",
                "versionType": "custom"
              }
            ]
          },
          {
            "platforms": [
              "x64-based Systems"
            ],
            "product": "Microsoft Exchange Server 2016 Cumulative Update 11",
            "vendor": "Microsoft",
            "versions": [
              {
                "lessThan": "15.01.1591.018",
                "status": "affected",
                "version": "15.01.0",
                "versionType": "custom"
              }
            ]
          },
          {
            "platforms": [
              "x64-based Systems"
            ],
            "product": "Microsoft Exchange Server 2016 Cumulative Update 12",
            "vendor": "Microsoft",
            "versions": [
              {
                "lessThan": "15.01.1713.010",
                "status": "affected",
                "version": "15.01.0",
                "versionType": "custom"
              }
            ]
          },
          {
            "platforms": [
              "x64-based Systems"
            ],
            "product": "Microsoft Exchange Server 2016 Cumulative Update 13",
            "vendor": "Microsoft",
            "versions": [
              {
                "lessThan": "15.01.1779.008",
                "status": "affected",
                "version": "15.01.0",
                "versionType": "custom"
              }
            ]
          },
          {
            "platforms": [
              "x64-based Systems"
            ],
            "product": "Microsoft Exchange Server 2016 Cumulative Update 14",
            "vendor": "Microsoft",
            "versions": [
              {
                "lessThan": "15.01.1847.012",
                "status": "affected",
                "version": "15.01.0",
                "versionType": "custom"
              }
            ]
          },
          {
            "platforms": [
              "x64-based Systems"
            ],
            "product": "Microsoft Exchange Server 2016 Cumulative Update 15",
            "vendor": "Microsoft",
            "versions": [
              {
                "lessThan": "15.01.1913.012",
                "status": "affected",
                "version": "15.01.0",
                "versionType": "custom"
              }
            ]
          },
          {
            "platforms": [
              "x64-based Systems"
            ],
            "product": "Microsoft Exchange Server 2016 Cumulative Update 16",
            "vendor": "Microsoft",
            "versions": [
              {
                "lessThan": "15.01.1979.008",
                "status": "affected",
                "version": "15.01.0",
                "versionType": "custom"
              }
            ]
          },
          {
            "platforms": [
              "x64-based Systems"
            ],
            "product": "Microsoft Exchange Server 2016 Cumulative Update 17",
            "vendor": "Microsoft",
            "versions": [
              {
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              }
            ]
          },
          {
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              "x64-based Systems"
            ],
            "product": "Microsoft Exchange Server 2019 Cumulative Update 5",
            "vendor": "Microsoft",
            "versions": [
              {
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                "status": "affected",
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                "versionType": "custom"
              }
            ]
          },
          {
            "platforms": [
              "x64-based Systems"
            ],
            "product": "Microsoft Exchange Server 2019 Cumulative Update 6",
            "vendor": "Microsoft",
            "versions": [
              {
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                "status": "affected",
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                "versionType": "custom"
              }
            ]
          },
          {
            "platforms": [
              "x64-based Systems"
            ],
            "product": "Microsoft Exchange Server 2019 Cumulative Update 7",
            "vendor": "Microsoft",
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              {
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                "status": "affected",
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                "versionType": "custom"
              }
            ]
          },
          {
            "platforms": [
              "x64-based Systems"
            ],
            "product": "Microsoft Exchange Server 2019 Cumulative Update 8",
            "vendor": "Microsoft",
            "versions": [
              {
                "lessThan": "15.02.0792.010",
                "status": "affected",
                "version": "15.02.0",
                "versionType": "custom"
              }
            ]
          }
        ],
        "source": "secure@microsoft.com"
      }
    ],
    "cisaActionDue": "2022-05-03",
    "cisaExploitAdd": "2021-11-03",
    "cisaRequiredAction": "Apply updates per vendor instructions.",
    "cisaVulnerabilityName": "Microsoft Exchange Server Remote Code Execution Vulnerability",
    "configurations": [
      {
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              }
            ],
            "negate": false,
            "operator": "OR"
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        ]
      }
    ],
    "cveTags": [],
    "descriptions": [
      {
        "lang": "en",
        "value": "Microsoft Exchange Server Remote Code Execution Vulnerability"
      },
      {
        "lang": "es",
        "value": "Una Vulnerabilidad de Ejecución de código remota de Microsoft Exchange Server. Este ID de CVE es diferente de CVE-2021-26412, CVE-2021-26854, CVE-2021-26855, CVE-2021-26857, CVE-2021-27065, CVE-2021-27078"
      }
    ],
    "id": "CVE-2021-26858",
    "lastModified": "2026-10-01T21:17:16.777",
    "metrics": {
      "cvssMetricV2": [
        {
          "acInsufInfo": false,
          "baseSeverity": "MEDIUM",
          "cvssData": {
            "accessComplexity": "MEDIUM",
            "accessVector": "NETWORK",
            "authentication": "NONE",
            "availabilityImpact": "PARTIAL",
            "baseScore": 6.8,
            "confidentialityImpact": "PARTIAL",
            "integrityImpact": "PARTIAL",
            "vectorString": "AV:N/AC:M/Au:N/C:P/I:P/A:P",
            "version": "2.0"
          },
          "exploitabilityScore": 8.6,
          "impactScore": 6.4,
          "obtainAllPrivilege": false,
          "obtainOtherPrivilege": false,
          "obtainUserPrivilege": false,
          "source": "nvd@nist.gov",
          "type": "Primary",
          "userInteractionRequired": true
        }
      ],
      "cvssMetricV31": [
        {
          "cvssData": {
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            "attackVector": "LOCAL",
            "availabilityImpact": "HIGH",
            "baseScore": 7.8,
            "baseSeverity": "HIGH",
            "confidentialityImpact": "HIGH",
            "integrityImpact": "HIGH",
            "privilegesRequired": "NONE",
            "scope": "UNCHANGED",
            "userInteraction": "REQUIRED",
            "vectorString": "CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H",
            "version": "3.1"
          },
          "exploitabilityScore": 1.8,
          "impactScore": 5.9,
          "source": "secure@microsoft.com",
          "type": "Secondary"
        },
        {
          "cvssData": {
            "attackComplexity": "LOW",
            "attackVector": "LOCAL",
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            "baseScore": 7.8,
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            "confidentialityImpact": "HIGH",
            "integrityImpact": "HIGH",
            "privilegesRequired": "NONE",
            "scope": "UNCHANGED",
            "userInteraction": "REQUIRED",
            "vectorString": "CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H",
            "version": "3.1"
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          "source": "nvd@nist.gov",
          "type": "Secondary"
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      ],
      "ssvcV203": [
        {
          "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "ssvcData": {
            "id": "CVE-2021-26858",
            "options": [
              {
                "exploitation": "active"
              },
              {
                "automatable": "yes"
              },
              {
                "technicalImpact": "total"
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            ],
            "role": "CISA Coordinator",
            "timestamp": "2026-08-12T03:55:36.937537Z",
            "version": "2.0.3"
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      ]
    },
    "published": "2021-03-03T00:15:12.227",
    "references": [
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        "tags": [
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          "Vendor Advisory"
        ],
        "url": "https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-26858"
      },
      {
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        "tags": [
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      },
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "tags": [
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        ],
        "url": "https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-26858"
      }
    ],
    "sourceIdentifier": "secure@microsoft.com",
    "vulnStatus": "Analyzed",
    "weaknesses": [
      {
        "description": [
          {
            "lang": "en",
            "value": "NVD-CWE-noinfo"
          }
        ],
        "source": "nvd@nist.gov",
        "type": "Primary"
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    ]
  }
}
—
Forensic triage
forensic_triage
CISA Known Exploited Vulnerabilitiesfalse
receipt
Source
CISA Known Exploited Vulnerabilities
Its words
No
Read by
field:forensicTriage
Said since
2026-09-28 11:44 UTC
Last answered
2026-10-06 17:36 UTC
What the source handed over
{
  "cveID": "CVE-2021-26858",
  "cwes": "",
  "dateAdded": "2021-11-03",
  "dueDate": "2022-05-03",
  "forensicTriage": "No",
  "knownRansomwareCampaignUse": "Known",
  "notes": "Reference CISA's ED 21-02 (https://www.cisa.gov/news-events/directives/ed-21-02-mitigate-microsoft-exchange-premises-product-vulnerabilities) for further guidance and requirements. Note: The due date for addressing this vulnerability aligns with the requirements outlined in ED 21-02. https://nvd.nist.gov/vuln/detail/CVE-2021-26858",
  "product": "Exchange Server",
  "requiredAction": "Apply updates per vendor instructions.",
  "shortDescription": "Microsoft Exchange Server contains an unspecified vulnerability that allows for remote code execution. This vulnerability is part of the ProxyLogon exploit chain.",
  "vendorProject": "Microsoft",
  "vulnerabilityName": "Microsoft Exchange Server Remote Code Execution Vulnerability"
}
—
Known ransomware campaign use
known_ransomware_campaign_use
CISA Known Exploited VulnerabilitiesKnown
receipt
Source
CISA Known Exploited Vulnerabilities
Its words
Known
Read by
field:knownRansomwareCampaignUse
Said since
2026-09-28 11:44 UTC
Last answered
2026-10-06 17:36 UTC
What the source handed over
{
  "cveID": "CVE-2021-26858",
  "cwes": "",
  "dateAdded": "2021-11-03",
  "dueDate": "2022-05-03",
  "forensicTriage": "No",
  "knownRansomwareCampaignUse": "Known",
  "notes": "Reference CISA's ED 21-02 (https://www.cisa.gov/news-events/directives/ed-21-02-mitigate-microsoft-exchange-premises-product-vulnerabilities) for further guidance and requirements. Note: The due date for addressing this vulnerability aligns with the requirements outlined in ED 21-02. https://nvd.nist.gov/vuln/detail/CVE-2021-26858",
  "product": "Exchange Server",
  "requiredAction": "Apply updates per vendor instructions.",
  "shortDescription": "Microsoft Exchange Server contains an unspecified vulnerability that allows for remote code execution. This vulnerability is part of the ProxyLogon exploit chain.",
  "vendorProject": "Microsoft",
  "vulnerabilityName": "Microsoft Exchange Server Remote Code Execution Vulnerability"
}
—
Product
product
different words		CISA Known Exploited VulnerabilitiesExchange Server
receipt
Source
CISA Known Exploited Vulnerabilities
Its words
Exchange Server
Read by
field:product
Said since
2026-09-28 11:44 UTC
Last answered
2026-10-06 17:36 UTC
What the source handed over
{
  "cveID": "CVE-2021-26858",
  "cwes": "",
  "dateAdded": "2021-11-03",
  "dueDate": "2022-05-03",
  "forensicTriage": "No",
  "knownRansomwareCampaignUse": "Known",
  "notes": "Reference CISA's ED 21-02 (https://www.cisa.gov/news-events/directives/ed-21-02-mitigate-microsoft-exchange-premises-product-vulnerabilities) for further guidance and requirements. Note: The due date for addressing this vulnerability aligns with the requirements outlined in ED 21-02. https://nvd.nist.gov/vuln/detail/CVE-2021-26858",
  "product": "Exchange Server",
  "requiredAction": "Apply updates per vendor instructions.",
  "shortDescription": "Microsoft Exchange Server contains an unspecified vulnerability that allows for remote code execution. This vulnerability is part of the ProxyLogon exploit chain.",
  "vendorProject": "Microsoft",
  "vulnerabilityName": "Microsoft Exchange Server Remote Code Execution Vulnerability"
}
—
Product
product
different words		NVDMicrosoft Exchange Server 2013 Cumulative Update 21
receipt
Source
NVD
Its words
Microsoft Exchange Server 2013 Cumulative Update 21
Read by
field:cve.affected[].affectedData[].product
Said since
2026-10-02 12:00 UTC
Last answered
2026-10-06 12:41 UTC
Original
open at the source
What the source handed over
{
  "cve": {
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      {
        "affectedData": [
          {
            "platforms": [
              "x64-based Systems"
            ],
            "product": "Microsoft Exchange Server 2013 Cumulative Update 21",
            "vendor": "Microsoft",
            "versions": [
              {
                "lessThan": "15.00.1395.012",
                "status": "affected",
                "version": "15.00.0",
                "versionType": "custom"
              }
            ]
          },
          {
            "platforms": [
              "x64-based Systems"
            ],
            "product": "Microsoft Exchange Server 2013 Cumulative Update 22",
            "vendor": "Microsoft",
            "versions": [
              {
                "lessThan": "15.00.1473.006",
                "status": "affected",
                "version": "15.00.0",
                "versionType": "custom"
              }
            ]
          },
          {
            "platforms": [
              "x64-based Systems"
            ],
            "product": "Microsoft Exchange Server 2013 Cumulative Update 23",
            "vendor": "Microsoft",
            "versions": [
              {
                "lessThan": "15.00.1497.012",
                "status": "affected",
                "version": "15.00.0",
                "versionType": "custom"
              }
            ]
          },
          {
            "platforms": [
              "x64-based Systems"
            ],
            "product": "Microsoft Exchange Server 2016 Cumulative Update 10",
            "vendor": "Microsoft",
            "versions": [
              {
                "lessThan": "15.01.1531.012",
                "status": "affected",
                "version": "15.01.0",
                "versionType": "custom"
              }
            ]
          },
          {
            "platforms": [
              "x64-based Systems"
            ],
            "product": "Microsoft Exchange Server 2016 Cumulative Update 11",
            "vendor": "Microsoft",
            "versions": [
              {
                "lessThan": "15.01.1591.018",
                "status": "affected",
                "version": "15.01.0",
                "versionType": "custom"
              }
            ]
          },
          {
            "platforms": [
              "x64-based Systems"
            ],
            "product": "Microsoft Exchange Server 2016 Cumulative Update 12",
            "vendor": "Microsoft",
            "versions": [
              {
                "lessThan": "15.01.1713.010",
                "status": "affected",
                "version": "15.01.0",
                "versionType": "custom"
              }
            ]
          },
          {
            "platforms": [
              "x64-based Systems"
            ],
            "product": "Microsoft Exchange Server 2016 Cumulative Update 13",
            "vendor": "Microsoft",
            "versions": [
              {
                "lessThan": "15.01.1779.008",
                "status": "affected",
                "version": "15.01.0",
                "versionType": "custom"
              }
            ]
          },
          {
            "platforms": [
              "x64-based Systems"
            ],
            "product": "Microsoft Exchange Server 2016 Cumulative Update 14",
            "vendor": "Microsoft",
            "versions": [
              {
                "lessThan": "15.01.1847.012",
                "status": "affected",
                "version": "15.01.0",
                "versionType": "custom"
              }
            ]
          },
          {
            "platforms": [
              "x64-based Systems"
            ],
            "product": "Microsoft Exchange Server 2016 Cumulative Update 15",
            "vendor": "Microsoft",
            "versions": [
              {
                "lessThan": "15.01.1913.012",
                "status": "affected",
                "version": "15.01.0",
                "versionType": "custom"
              }
            ]
          },
          {
            "platforms": [
              "x64-based Systems"
            ],
            "product": "Microsoft Exchange Server 2016 Cumulative Update 16",
            "vendor": "Microsoft",
            "versions": [
              {
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    "cveTags": [],
    "descriptions": [
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        "value": "Microsoft Exchange Server Remote Code Execution Vulnerability"
      },
      {
        "lang": "es",
        "value": "Una Vulnerabilidad de Ejecución de código remota de Microsoft Exchange Server. Este ID de CVE es diferente de CVE-2021-26412, CVE-2021-26854, CVE-2021-26855, CVE-2021-26857, CVE-2021-27065, CVE-2021-27078"
      }
    ],
    "id": "CVE-2021-26858",
    "lastModified": "2026-10-01T21:17:16.777",
    "metrics": {
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          "baseSeverity": "MEDIUM",
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                "technicalImpact": "total"
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            "timestamp": "2026-08-12T03:55:36.937537Z",
            "version": "2.0.3"
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    },
    "published": "2021-03-03T00:15:12.227",
    "references": [
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        "source": "secure@microsoft.com",
        "tags": [
          "Patch",
          "Vendor Advisory"
        ],
        "url": "https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-26858"
      },
      {
        "source": "af854a3a-2127-422b-91ae-364da2661108",
        "tags": [
          "Patch",
          "Vendor Advisory"
        ],
        "url": "https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-26858"
      },
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "tags": [
          "US Government Resource"
        ],
        "url": "https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-26858"
      }
    ],
    "sourceIdentifier": "secure@microsoft.com",
    "vulnStatus": "Analyzed",
    "weaknesses": [
      {
        "description": [
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            "lang": "en",
            "value": "NVD-CWE-noinfo"
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        "source": "nvd@nist.gov",
        "type": "Primary"
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    ]
  }
}
—
Severity
severity
NVDHIGH
From 7.0 to 8.9.
receipt
Source
NVD
Its words
HIGH
Read by
field:cve.metrics.cvssMetricV31[type=Primary].cvssData.baseSeverity || field:cve.metrics.cvssMetricV31[].cvssData.baseSeverity
Said since
2026-10-06 11:54 UTC
Last answered
2026-10-06 12:41 UTC
Original
open at the source
2026-10-06 11:54 UTCHIGH
2026-10-02 12:00 UTC—
What the source handed over
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            "negate": false,
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    "cveTags": [],
    "descriptions": [
      {
        "lang": "en",
        "value": "Microsoft Exchange Server Remote Code Execution Vulnerability"
      },
      {
        "lang": "es",
        "value": "Una Vulnerabilidad de Ejecución de código remota de Microsoft Exchange Server. Este ID de CVE es diferente de CVE-2021-26412, CVE-2021-26854, CVE-2021-26855, CVE-2021-26857, CVE-2021-27065, CVE-2021-27078"
      }
    ],
    "id": "CVE-2021-26858",
    "lastModified": "2026-10-01T21:17:16.777",
    "metrics": {
      "cvssMetricV2": [
        {
          "acInsufInfo": false,
          "baseSeverity": "MEDIUM",
          "cvssData": {
            "accessComplexity": "MEDIUM",
            "accessVector": "NETWORK",
            "authentication": "NONE",
            "availabilityImpact": "PARTIAL",
            "baseScore": 6.8,
            "confidentialityImpact": "PARTIAL",
            "integrityImpact": "PARTIAL",
            "vectorString": "AV:N/AC:M/Au:N/C:P/I:P/A:P",
            "version": "2.0"
          },
          "exploitabilityScore": 8.6,
          "impactScore": 6.4,
          "obtainAllPrivilege": false,
          "obtainOtherPrivilege": false,
          "obtainUserPrivilege": false,
          "source": "nvd@nist.gov",
          "type": "Primary",
          "userInteractionRequired": true
        }
      ],
      "cvssMetricV31": [
        {
          "cvssData": {
            "attackComplexity": "LOW",
            "attackVector": "LOCAL",
            "availabilityImpact": "HIGH",
            "baseScore": 7.8,
            "baseSeverity": "HIGH",
            "confidentialityImpact": "HIGH",
            "integrityImpact": "HIGH",
            "privilegesRequired": "NONE",
            "scope": "UNCHANGED",
            "userInteraction": "REQUIRED",
            "vectorString": "CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H",
            "version": "3.1"
          },
          "exploitabilityScore": 1.8,
          "impactScore": 5.9,
          "source": "secure@microsoft.com",
          "type": "Secondary"
        },
        {
          "cvssData": {
            "attackComplexity": "LOW",
            "attackVector": "LOCAL",
            "availabilityImpact": "HIGH",
            "baseScore": 7.8,
            "baseSeverity": "HIGH",
            "confidentialityImpact": "HIGH",
            "integrityImpact": "HIGH",
            "privilegesRequired": "NONE",
            "scope": "UNCHANGED",
            "userInteraction": "REQUIRED",
            "vectorString": "CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H",
            "version": "3.1"
          },
          "exploitabilityScore": 1.8,
          "impactScore": 5.9,
          "source": "nvd@nist.gov",
          "type": "Secondary"
        }
      ],
      "ssvcV203": [
        {
          "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "ssvcData": {
            "id": "CVE-2021-26858",
            "options": [
              {
                "exploitation": "active"
              },
              {
                "automatable": "yes"
              },
              {
                "technicalImpact": "total"
              }
            ],
            "role": "CISA Coordinator",
            "timestamp": "2026-08-12T03:55:36.937537Z",
            "version": "2.0.3"
          }
        }
      ]
    },
    "published": "2021-03-03T00:15:12.227",
    "references": [
      {
        "source": "secure@microsoft.com",
        "tags": [
          "Patch",
          "Vendor Advisory"
        ],
        "url": "https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-26858"
      },
      {
        "source": "af854a3a-2127-422b-91ae-364da2661108",
        "tags": [
          "Patch",
          "Vendor Advisory"
        ],
        "url": "https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-26858"
      },
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "tags": [
          "US Government Resource"
        ],
        "url": "https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-26858"
      }
    ],
    "sourceIdentifier": "secure@microsoft.com",
    "vulnStatus": "Analyzed",
    "weaknesses": [
      {
        "description": [
          {
            "lang": "en",
            "value": "NVD-CWE-noinfo"
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        "source": "nvd@nist.gov",
        "type": "Primary"
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    ]
  }
}
high
Status
status
NVDAnalyzed
receipt
Source
NVD
Its words
Analyzed
Read by
field:cve.vulnStatus
Said since
2026-10-02 12:00 UTC
Last answered
2026-10-06 12:41 UTC
Original
open at the source
What the source handed over
{
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      {
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            ],
            "negate": false,
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        ]
      }
    ],
    "cveTags": [],
    "descriptions": [
      {
        "lang": "en",
        "value": "Microsoft Exchange Server Remote Code Execution Vulnerability"
      },
      {
        "lang": "es",
        "value": "Una Vulnerabilidad de Ejecución de código remota de Microsoft Exchange Server. Este ID de CVE es diferente de CVE-2021-26412, CVE-2021-26854, CVE-2021-26855, CVE-2021-26857, CVE-2021-27065, CVE-2021-27078"
      }
    ],
    "id": "CVE-2021-26858",
    "lastModified": "2026-10-01T21:17:16.777",
    "metrics": {
      "cvssMetricV2": [
        {
          "acInsufInfo": false,
          "baseSeverity": "MEDIUM",
          "cvssData": {
            "accessComplexity": "MEDIUM",
            "accessVector": "NETWORK",
            "authentication": "NONE",
            "availabilityImpact": "PARTIAL",
            "baseScore": 6.8,
            "confidentialityImpact": "PARTIAL",
            "integrityImpact": "PARTIAL",
            "vectorString": "AV:N/AC:M/Au:N/C:P/I:P/A:P",
            "version": "2.0"
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          "exploitabilityScore": 8.6,
          "impactScore": 6.4,
          "obtainAllPrivilege": false,
          "obtainOtherPrivilege": false,
          "obtainUserPrivilege": false,
          "source": "nvd@nist.gov",
          "type": "Primary",
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        }
      ],
      "cvssMetricV31": [
        {
          "cvssData": {
            "attackComplexity": "LOW",
            "attackVector": "LOCAL",
            "availabilityImpact": "HIGH",
            "baseScore": 7.8,
            "baseSeverity": "HIGH",
            "confidentialityImpact": "HIGH",
            "integrityImpact": "HIGH",
            "privilegesRequired": "NONE",
            "scope": "UNCHANGED",
            "userInteraction": "REQUIRED",
            "vectorString": "CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H",
            "version": "3.1"
          },
          "exploitabilityScore": 1.8,
          "impactScore": 5.9,
          "source": "secure@microsoft.com",
          "type": "Secondary"
        },
        {
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            "attackVector": "LOCAL",
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            "baseScore": 7.8,
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            "confidentialityImpact": "HIGH",
            "integrityImpact": "HIGH",
            "privilegesRequired": "NONE",
            "scope": "UNCHANGED",
            "userInteraction": "REQUIRED",
            "vectorString": "CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H",
            "version": "3.1"
          },
          "exploitabilityScore": 1.8,
          "impactScore": 5.9,
          "source": "nvd@nist.gov",
          "type": "Secondary"
        }
      ],
      "ssvcV203": [
        {
          "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "ssvcData": {
            "id": "CVE-2021-26858",
            "options": [
              {
                "exploitation": "active"
              },
              {
                "automatable": "yes"
              },
              {
                "technicalImpact": "total"
              }
            ],
            "role": "CISA Coordinator",
            "timestamp": "2026-08-12T03:55:36.937537Z",
            "version": "2.0.3"
          }
        }
      ]
    },
    "published": "2021-03-03T00:15:12.227",
    "references": [
      {
        "source": "secure@microsoft.com",
        "tags": [
          "Patch",
          "Vendor Advisory"
        ],
        "url": "https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-26858"
      },
      {
        "source": "af854a3a-2127-422b-91ae-364da2661108",
        "tags": [
          "Patch",
          "Vendor Advisory"
        ],
        "url": "https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-26858"
      },
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "tags": [
          "US Government Resource"
        ],
        "url": "https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-26858"
      }
    ],
    "sourceIdentifier": "secure@microsoft.com",
    "vulnStatus": "Analyzed",
    "weaknesses": [
      {
        "description": [
          {
            "lang": "en",
            "value": "NVD-CWE-noinfo"
          }
        ],
        "source": "nvd@nist.gov",
        "type": "Primary"
      }
    ]
  }
}
—
Technical impact
technical_impact
NVDtotal
The attacker gains full control of the component, or all of its information.
receipt
Source
NVD
Its words
total
Read by
field:cve.metrics.ssvcV203[].ssvcData.options[].technicalImpact
Said since
2026-10-06 11:54 UTC
Last answered
2026-10-06 12:41 UTC
Original
open at the source
2026-10-06 11:54 UTCtotal
2026-10-02 12:00 UTC—
What the source handed over
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            "negate": false,
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    ],
    "cveTags": [],
    "descriptions": [
      {
        "lang": "en",
        "value": "Microsoft Exchange Server Remote Code Execution Vulnerability"
      },
      {
        "lang": "es",
        "value": "Una Vulnerabilidad de Ejecución de código remota de Microsoft Exchange Server. Este ID de CVE es diferente de CVE-2021-26412, CVE-2021-26854, CVE-2021-26855, CVE-2021-26857, CVE-2021-27065, CVE-2021-27078"
      }
    ],
    "id": "CVE-2021-26858",
    "lastModified": "2026-10-01T21:17:16.777",
    "metrics": {
      "cvssMetricV2": [
        {
          "acInsufInfo": false,
          "baseSeverity": "MEDIUM",
          "cvssData": {
            "accessComplexity": "MEDIUM",
            "accessVector": "NETWORK",
            "authentication": "NONE",
            "availabilityImpact": "PARTIAL",
            "baseScore": 6.8,
            "confidentialityImpact": "PARTIAL",
            "integrityImpact": "PARTIAL",
            "vectorString": "AV:N/AC:M/Au:N/C:P/I:P/A:P",
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          "exploitabilityScore": 8.6,
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          "obtainAllPrivilege": false,
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            "scope": "UNCHANGED",
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            "vectorString": "CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H",
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          "source": "secure@microsoft.com",
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          "source": "nvd@nist.gov",
          "type": "Secondary"
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      ],
      "ssvcV203": [
        {
          "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "ssvcData": {
            "id": "CVE-2021-26858",
            "options": [
              {
                "exploitation": "active"
              },
              {
                "automatable": "yes"
              },
              {
                "technicalImpact": "total"
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            ],
            "role": "CISA Coordinator",
            "timestamp": "2026-08-12T03:55:36.937537Z",
            "version": "2.0.3"
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    "published": "2021-03-03T00:15:12.227",
    "references": [
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        "tags": [
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          "Vendor Advisory"
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        "url": "https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-26858"
      },
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        "source": "af854a3a-2127-422b-91ae-364da2661108",
        "tags": [
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          "Vendor Advisory"
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      {
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        "tags": [
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        "url": "https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-26858"
      }
    ],
    "sourceIdentifier": "secure@microsoft.com",
    "vulnStatus": "Analyzed",
    "weaknesses": [
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        "description": [
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            "value": "NVD-CWE-noinfo"
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        "source": "nvd@nist.gov",
        "type": "Primary"
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    ]
  }
}
—
Vendor
vendor
CISA Known Exploited VulnerabilitiesMicrosoft
receipt
Source
CISA Known Exploited Vulnerabilities
Last answered
2026-10-06 17:36 UTC
What the source handed over
{
  "cveID": "CVE-2021-26858",
  "cwes": "",
  "dateAdded": "2021-11-03",
  "dueDate": "2022-05-03",
  "forensicTriage": "No",
  "knownRansomwareCampaignUse": "Known",
  "notes": "Reference CISA's ED 21-02 (https://www.cisa.gov/news-events/directives/ed-21-02-mitigate-microsoft-exchange-premises-product-vulnerabilities) for further guidance and requirements. Note: The due date for addressing this vulnerability aligns with the requirements outlined in ED 21-02. https://nvd.nist.gov/vuln/detail/CVE-2021-26858",
  "product": "Exchange Server",
  "requiredAction": "Apply updates per vendor instructions.",
  "shortDescription": "Microsoft Exchange Server contains an unspecified vulnerability that allows for remote code execution. This vulnerability is part of the ProxyLogon exploit chain.",
  "vendorProject": "Microsoft",
  "vulnerabilityName": "Microsoft Exchange Server Remote Code Execution Vulnerability"
}
—
Vendor
vendor
NVDMicrosoft
receipt
Source
NVD
Its words
Microsoft
Read by
field:cve.affected[].affectedData[].vendor
Said since
2026-10-02 12:00 UTC
Last answered
2026-10-06 12:41 UTC
Original
open at the source
What the source handed over
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                "matchCriteriaId": "D4AB3C25-CEA8-4D66-AEE4-953C8B17911A",
                "vulnerable": true
              },
              {
                "criteria": "cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_7:*:*:*:*:*:*",
                "matchCriteriaId": "36CE5C6D-9A04-41F5-AE7C-265779833649",
                "vulnerable": true
              },
              {
                "criteria": "cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_8:*:*:*:*:*:*",
                "matchCriteriaId": "44ECF39A-1DE1-4870-A494-06A53494338D",
                "vulnerable": true
              }
            ],
            "negate": false,
            "operator": "OR"
          }
        ]
      }
    ],
    "cveTags": [],
    "descriptions": [
      {
        "lang": "en",
        "value": "Microsoft Exchange Server Remote Code Execution Vulnerability"
      },
      {
        "lang": "es",
        "value": "Una Vulnerabilidad de Ejecución de código remota de Microsoft Exchange Server. Este ID de CVE es diferente de CVE-2021-26412, CVE-2021-26854, CVE-2021-26855, CVE-2021-26857, CVE-2021-27065, CVE-2021-27078"
      }
    ],
    "id": "CVE-2021-26858",
    "lastModified": "2026-10-01T21:17:16.777",
    "metrics": {
      "cvssMetricV2": [
        {
          "acInsufInfo": false,
          "baseSeverity": "MEDIUM",
          "cvssData": {
            "accessComplexity": "MEDIUM",
            "accessVector": "NETWORK",
            "authentication": "NONE",
            "availabilityImpact": "PARTIAL",
            "baseScore": 6.8,
            "confidentialityImpact": "PARTIAL",
            "integrityImpact": "PARTIAL",
            "vectorString": "AV:N/AC:M/Au:N/C:P/I:P/A:P",
            "version": "2.0"
          },
          "exploitabilityScore": 8.6,
          "impactScore": 6.4,
          "obtainAllPrivilege": false,
          "obtainOtherPrivilege": false,
          "obtainUserPrivilege": false,
          "source": "nvd@nist.gov",
          "type": "Primary",
          "userInteractionRequired": true
        }
      ],
      "cvssMetricV31": [
        {
          "cvssData": {
            "attackComplexity": "LOW",
            "attackVector": "LOCAL",
            "availabilityImpact": "HIGH",
            "baseScore": 7.8,
            "baseSeverity": "HIGH",
            "confidentialityImpact": "HIGH",
            "integrityImpact": "HIGH",
            "privilegesRequired": "NONE",
            "scope": "UNCHANGED",
            "userInteraction": "REQUIRED",
            "vectorString": "CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H",
            "version": "3.1"
          },
          "exploitabilityScore": 1.8,
          "impactScore": 5.9,
          "source": "secure@microsoft.com",
          "type": "Secondary"
        },
        {
          "cvssData": {
            "attackComplexity": "LOW",
            "attackVector": "LOCAL",
            "availabilityImpact": "HIGH",
            "baseScore": 7.8,
            "baseSeverity": "HIGH",
            "confidentialityImpact": "HIGH",
            "integrityImpact": "HIGH",
            "privilegesRequired": "NONE",
            "scope": "UNCHANGED",
            "userInteraction": "REQUIRED",
            "vectorString": "CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H",
            "version": "3.1"
          },
          "exploitabilityScore": 1.8,
          "impactScore": 5.9,
          "source": "nvd@nist.gov",
          "type": "Secondary"
        }
      ],
      "ssvcV203": [
        {
          "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "ssvcData": {
            "id": "CVE-2021-26858",
            "options": [
              {
                "exploitation": "active"
              },
              {
                "automatable": "yes"
              },
              {
                "technicalImpact": "total"
              }
            ],
            "role": "CISA Coordinator",
            "timestamp": "2026-08-12T03:55:36.937537Z",
            "version": "2.0.3"
          }
        }
      ]
    },
    "published": "2021-03-03T00:15:12.227",
    "references": [
      {
        "source": "secure@microsoft.com",
        "tags": [
          "Patch",
          "Vendor Advisory"
        ],
        "url": "https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-26858"
      },
      {
        "source": "af854a3a-2127-422b-91ae-364da2661108",
        "tags": [
          "Patch",
          "Vendor Advisory"
        ],
        "url": "https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-26858"
      },
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "tags": [
          "US Government Resource"
        ],
        "url": "https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-26858"
      }
    ],
    "sourceIdentifier": "secure@microsoft.com",
    "vulnStatus": "Analyzed",
    "weaknesses": [
      {
        "description": [
          {
            "lang": "en",
            "value": "NVD-CWE-noinfo"
          }
        ],
        "source": "nvd@nist.gov",
        "type": "Primary"
      }
    ]
  }
}
—
Every claim, by kind

vulnerability

Microsoft Exchange Server Remote Code Execution Vulnerability
zetlyn/cve-kev · 2021-11-03
due_date 2022-05-03 exploited yes forensic_triage false known_ransomware_campaign_use Known product Exchange Server vendor Microsoft
Microsoft Exchange Server Remote Code Execution Vulnerability
zetlyn/cve-nvd · 2021-03-03
automatable yes cvss 7.8 cvss_vector CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H exploitation active fixed_in 15.00.1395.012, 15.00.1473.006, 15.00.1497.012, 15.01.1531.012, 15.01.1591.018, 15.01.1713.010, 15.01.1779.008, 15.01.1847.012, 15.01.1913.012, 15.01.1979.008, 15.01.2044.013, 15.01.2106.013, 15.01.2176.009, 15.01.1415.010, 15.01.1466.016, 15.02.0221.018, 15.01.1979.006, 15.02.0397.011, 15.02.0464.015, 15.02.0659.012, 15.02.0595.008, 15.02.0529.013, 15.02.0721.013, 15.02.0792.010 product Microsoft Exchange Server 2013 Cumulative Update 21 severity HIGH status Analyzed technical_impact total vendor Microsoft source
CVE-2021-26858
zetlyn/cve-epss · 2026-10-05
epss 0.93651 epss_percentile 0.99842 source