CVE-2026-1999

Description

An incorrect authorization vulnerability was identified in GitHub Enterprise Server that allowed an attacker to merge their own pull request into a repository without having push access by exploiting an authorization bypass in the enable_auto_merge mutation for pull requests. This issue only affected repositories that allow forking as the attack relies on opening a pull request from an attacker-controlled fork into the target repository. Exploitation was only possible in specific scenarios. It required a clean pull request status and only applied to branches without branch protection rules enabled. This vulnerability affected GitHub Enterprise Server versions prior to 3.19.2, 3.18.5, and 3.17.11, and was fixed in versions 3.19.2, 3.18.5, and 3.17.11. This vulnerability was reported via the GitHub Bug Bounty program.

PUBLISHED Reserved 2026-02-05 | Published 2026-02-18 | Updated 2026-02-18 | Assigner GitHub_P

Problem types

CWE-863 Incorrect Authorization

Product status

Credits

ahacker1 finder

References

docs.github.com/...nterprise-server@3.17/admin/release-notes release-notes

docs.github.com/...nterprise-server@3.18/admin/release-notes release-notes

docs.github.com/...nterprise-server@3.19/admin/release-notes release-notes

cve.org (CVE-2026-1999)

nvd.nist.gov (CVE-2026-1999)

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