CVE-2026-103620

Missing authorization in GitHub Enterprise Server allowed repository writers to replace default branches via GraphQL

State: Published
Severity: 6.0 Medium
Published: Oct 6, 2026
Updated: Oct 7, 2026
Reserved: Sep 30, 2026

Description

A missing authorization vulnerability was identified in GitHub Enterprise Server that allowed a repository collaborator with write access to delete the current default branch through the GraphQL API and cause an attacker-controlled branch to become the new default. In repositories that required pull-request review but did not restrict branch deletion, this bypassed the review requirement and caused fresh clones and default-branch API requests to use attacker-controlled content. This vulnerability affected supported GitHub Enterprise Server releases in the 3.18, 3.19, 3.20, 3.21, and 3.22 series and was fixed in versions 3.18.16, 3.19.13, 3.20.9, 3.21.7, and 3.22.2. This vulnerability was reported via the GitHub Bug Bounty program.

Scores

CVSS	Score	Vector	Source
4.0	6.0 Medium	CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N	GitHub_P

Weaknesses

CWE-862 Missing Authorization

Affected Products

Product	Versions
Enterprise ServerGitHub	3.18.0 to before 3.18.Affectedfrom 3.18.16Not affected 3.19.0 to before 3.19.Affectedfrom 3.19.13Not affected 3.20.0 to before 3.20.Affectedfrom 3.20.9Not affected 3.21.0 to before 3.21.Affectedfrom 3.21.7Not affected 3.22.0 to before 3.22.*Affectedfrom 3.22.2Not affected

References

https://docs.github.com/en/enterprise-server@3.18/admin/release-notes#3.18.16release-notes
https://docs.github.com/en/enterprise-server@3.19/admin/release-notes#3.19.13release-notes
https://docs.github.com/en/enterprise-server@3.20/admin/release-notes#3.20.9release-notes
https://docs.github.com/en/enterprise-server@3.21/admin/release-notes#3.21.7release-notes
https://docs.github.com/en/enterprise-server@3.22/admin/release-notes#3.22.2release-notes

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