CVE-2026-103620: Missing authorization in GitHub Enterprise Server allowed repository writers to replace default branches via GraphQL
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.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
GitHub Enterprise Serverto a version that resolves this vulnerability.Fixed in 3.18.16 - Upgrade
Upgrade
GitHub Enterprise Serverto a version that resolves this vulnerability.Fixed in 3.19.13 - Upgrade
Upgrade
GitHub Enterprise Serverto a version that resolves this vulnerability.Fixed in 3.20.9 - Upgrade
Upgrade
GitHub Enterprise Serverto a version that resolves this vulnerability.Fixed in 3.21.7 - Upgrade
Upgrade
GitHub Enterprise Serverto a version that resolves this vulnerability.Fixed in 3.22.2
Event History
Frequently Asked Questions
Which GitHub Enterprise Server versions need to be updated?
Supported releases in the 3.18 through 3.22 series were affected. The fixes are 3.18.16, 3.19.13, 3.20.9, 3.21.7, and 3.22.2.
What level of access would an attacker need?
The attacker would need collaborator write access to the target repository. Exploitation used the GraphQL API and did not require user interaction.
Which repositories face the most direct review-bypass risk?
Repositories that require pull-request review but do not restrict branch deletion are specifically affected by the review-bypass scenario. In those repositories, a writer could delete the default branch and cause an attacker-controlled branch to become the new default.
What can be done before an upgrade is available?
Restrict branch deletion for repositories where pull-request review is relied upon. This addresses the configuration condition identified for the review-bypass scenario.