High 8.9Published Apr 21, 2026

CVE-2026-5921Server-Side Request Forgery in GitHub Enterprise Server allowed extraction of sensitive environment variables via timing side-channel attack

Updated under an hour ago (Oct 28, 2026, 11:00 AM ET)

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It affects GitHub Enterprise Server. Add what you run to find out whether that includes you.

No exploitation reported and no EPSS estimate yet.

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Every CVE for GitHub Enterprise Server

Exploited in the last 30 days

A server-side request forgery (SSRF) vulnerability was identified in GitHub Enterprise Server that allowed an attacker to extract sensitive environment variables from the instance through a timing side-channel attack against the notebook rendering service. When private mode was disabled, the notebook viewer followed HTTP redirects without revalidating the destination host, enabling an unauthenticated SSRF to internal services. By chaining this with regex filter queries against an internal API and measuring response time differences, an attacker could infer secret values character by character. Exploitation required that private mode be disabled and that the attacker be able to chain the instance's open redirect endpoint through an external redirect to reach internal services. This vulnerability affected all versions of GitHub Enterprise Server prior to 3.21 and was fixed in versions 3.14.26, 3.15.21, 3.16.17, 3.17.14, 3.18.8, 3.19.5, and 3.20.1. This vulnerability was reported via the GitHub Bug Bounty program.

CVSS: 8.9 HIGH (v4.0, CNA)CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:H/VI:H/VA:L/SC:H/SI:H/SA:L/E:P
Weakness (CWE): CWE-918
Known exploited: Not in CISA's KEV catalog
EPSS (exploitation in the next 30 days): Not loaded for this CVE
Assigned by: GitHub_P
NVD analysis: Analyzed
Record last updated: Apr 22, 2026
First seen by InfoSec Signals: Oct 9, 2026

Affected products

Affected products

GitHub Enterprise Server github:enterprise_server (from the name)	from 3.14.0 before 3.14.26; fixed at 3.14.26; from 3.15.0 before 3.15.21; fixed at 3.15.21; from 3.16.0 before 3.16.17; fixed at 3.16.17; from 3.17.0 before 3.17.14; fixed at 3.17.14; from 3.18.0 before 3.18.8; fixed at 3.18.8; from 3.19.0 before 3.19.5; fixed at 3.19.5; from 3.20.0 before 3.20.1; fixed at 3.20.1	CNA record
github enterprise_server github:enterprise_server	before 3.14.26; from 3.15.0 before 3.15.21; from 3.16.0 before 3.16.17; from 3.17.0 before 3.17.14; from 3.18.0 before 3.18.8; from 3.19.0 before 3.19.5; 3.20.0	NVD

References

References

https://docs.github.com/en/enterprise-server@3.14/admin/release-notes#3.14.26	release-notes, vendor-advisory
https://docs.github.com/en/enterprise-server@3.15/admin/release-notes#3.15.21	release-notes, vendor-advisory
https://docs.github.com/en/enterprise-server@3.16/admin/release-notes#3.16.17	release-notes, vendor-advisory
https://docs.github.com/en/enterprise-server@3.17/admin/release-notes#3.17.14	release-notes, vendor-advisory
https://docs.github.com/en/enterprise-server@3.18/admin/release-notes#3.18.8	release-notes, vendor-advisory
https://docs.github.com/en/enterprise-server@3.19/admin/release-notes#3.19.5	release-notes, vendor-advisory
https://docs.github.com/en/enterprise-server@3.20/admin/release-notes#3.20.1	release-notes, vendor-advisory

The CVE record on cve.org NVD's entry

The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.