A server-side request forgery (SSRF) vulnerability was identified in the notebook viewer of GitHub Enterprise Server. The notebook viewer validated the scheme and host of a user-supplied URL but did not validate the port, allowing requests to be directed to internal services listening on other ports of the same appliance. Response bodies were not returned to the requester, but response timing acted as an oracle that allowed instance secrets to be extracted character by character. An extracted secret could then be used in a separate interaction with an internal service to obtain remote code execution on the appliance. Exploitation required network access to the instance and was unauthenticated when private mode was disabled, or required any authenticated user when private mode was enabled. This vulnerability affected GitHub Enterprise Server versions 3.17 through 3.22 and was fixed in versions 3.22.1, 3.21.6, 3.20.8, 3.19.12, 3.18.15, and 3.17.21. This vulnerability was reported through the GitHub Bug Bounty program.

zetlyn/cve-nvd vulnerability cve CVE-2026-77987 cpe cpe:2.3:a:github:enterprise_server:*:*:*:*:*:*:*:* known 2026-09-22

https://nvd.nist.gov/vuln/detail/CVE-2026-77987

Properties

cvss9.8
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Its words
9.8
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Said since
2026-10-03 00:06 UTC
Last answered
2026-10-04 18:16 UTC
Original
open at the source
2026-10-03 00:06 UTC9.8
2026-09-29 09:45 UTC—
What the source handed over
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Original
open at the source
2026-09-29 17:49 UTCEnterprise Server
2026-09-29 09:45 UTC—
What the source handed over
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Source
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Said since
2026-10-03 00:06 UTC
Last answered
2026-10-04 18:16 UTC
Original
open at the source
2026-10-03 00:06 UTCAnalyzed
2026-09-29 09:45 UTCAwaiting Analysis
What the source handed over
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vendorGitHub
receipt
Source
NVD
Its words
GitHub
Read by
field:cve.affected[].affectedData[].vendor
Said since
2026-09-29 17:49 UTC
Last answered
2026-10-04 18:16 UTC
Original
open at the source
2026-09-29 17:49 UTCGitHub
2026-09-29 09:45 UTC—
What the source handed over
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Text

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