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CVE-2026-5845: Improper authorization fallback allows scoped user-to-server token installation escape in GitHub Enterprise Server

• Severity: critical (CVSS 9.6 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.3% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-04-21 · updated 2026-10-26
• Weakness: CWE-639

Description

An improper authorization vulnerability in scoped user-to-server (ghu_) token authorization in GitHub Enterprise Server allows an authenticated attacker to access private repositories outside the intended installation scope, which can include write operations, via an authorization fallback that treated a revoked/deleted installation as a global installation context, which could be chained with token revocation timing and SSH push attribution to obtain and reuse a victim-scoped token. This vulnerability affected all versions of GitHub Enterprise Server prior to 3.21 and was fixed in versions 3.20.1, 3.19.5, 3.18.8, 3.17.14, 3.16.17, 3.15.21, and 3.14.26. This vulnerability was reported via the GitHub Bug Bounty program.

Affected products

• 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 — fixed in 3.14.26, 3.15.21, 3.16.17, 3.17.14, 3.18.8, 3.19.5

How to fix

Upgrade to a fixed version: GitHub Enterprise Server 3.14.26, 3.15.21, 3.16.17, 3.17.14. Check the vendor advisory for mitigations.

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

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