CVE-2026-5921
Description
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.
Predictions
Heuristic predictions, AS-IS, for prioritization only.
Mitigations
No mitigations published for this CVE yet.
The vendor-content worker queues fetches as references arrive (check back in a few minutes). Or — if you've already worked around this in production — publish your fix to the community-verified tier.
✚ Propose a mitigation on Community → Mitigations published via the community go through AI scoring + 2 human reviewers + 7-day silent objection window before landing here withsource_tier=community-verified.
Application impact
| Vendor | Product | Versions | Fixed |
|---|---|---|---|
| github | enterprise_server | {"endExcluding":"3.14.26"} | 3.14.26 |
| github | enterprise_server | 3.20.0 | |
References
- https://docs.github.com/en/enterprise-server@3.14/admin/release-notes#3.14.26
- https://docs.github.com/en/enterprise-server@3.15/admin/release-notes#3.15.21
- https://docs.github.com/en/enterprise-server@3.16/admin/release-notes#3.16.17
- https://docs.github.com/en/enterprise-server@3.17/admin/release-notes#3.17.14
- https://docs.github.com/en/enterprise-server@3.18/admin/release-notes#3.18.8
- https://docs.github.com/en/enterprise-server@3.19/admin/release-notes#3.19.5
- https://docs.github.com/en/enterprise-server@3.20/admin/release-notes#3.20.1
CWEs
CWE-918
Community-verified mitigations for this CVE will appear above when contributors publish them.
Verify integrity in audit chain (admin only). AS-IS.