An authentication bypass vulnerability was identified in GitHub Enterprise Server that allowed an unauthenticated attacker to create a local user account, bypassing the configured external identity provider. When external authentication was enabled, the signup endpoint did not properly enforce the authentication restriction, allowing account creation and session establishment without identity provider validation. The created account was limited to the default base permissions configured on the instance. Exploitation required network access to a GHES instance configured with an external authentication provider. This vulnerability affected all versions of GitHub Enterprise Server prior to 3.21 and was fixed in versions 3.20.2, 3.19.6, 3.18.9, 3.17.15, and 3.16.18.
Fix
Patch, vendor advisory and mitigation references on NVD 5
- https://docs.github.com/en/[email protected]/admin/release-notes#3.16.18 Release Notes, Vendor Advisory
- https://docs.github.com/en/[email protected]/admin/release-notes#3.17.15 Release Notes, Vendor Advisory
- https://docs.github.com/en/[email protected]/admin/release-notes#3.18.9 Release Notes, Vendor Advisory
- https://docs.github.com/en/[email protected]/admin/release-notes#3.19.6 Release Notes, Vendor Advisory
- https://docs.github.com/en/[email protected]/admin/release-notes#3.20.2 Release Notes, Vendor Advisory
Every line above is quoted from NVD, CISA, Microsoft, the vendor's own advisory or DISA; nothing is generated.
Change history 1
- First seenCVSS 6.3 · githubNVD modified 2026-10-26 20:10
Affected (CPE criteria) 1
cpe:2.3:a:github:enterprise_server:*:*:*:*:*:*:*:*
References 5
- https://docs.github.com/en/[email protected]/admin/release-notes#3.16.18 Release Notes, Vendor Advisory
- https://docs.github.com/en/[email protected]/admin/release-notes#3.17.15 Release Notes, Vendor Advisory
- https://docs.github.com/en/[email protected]/admin/release-notes#3.18.9 Release Notes, Vendor Advisory
- https://docs.github.com/en/[email protected]/admin/release-notes#3.19.6 Release Notes, Vendor Advisory
- https://docs.github.com/en/[email protected]/admin/release-notes#3.20.2 Release Notes, Vendor Advisory