CVE-2026-1999: github enterprise_server Incorrect Authorization

Vulnerability summary

CVE-2026-1999 is a high (CVSS 7.1) Incorrect Authorization vulnerability in github enterprise_server. EPSS estimates a 0.36% chance of exploitation in the next 30 days, higher than 28.3% of scored vulnerabilities.

Timeline

1. 18-02-2026
   PublishedVulnerability first disclosed.
2. 14-04-2026
   Last modifiedVulnerability information updated.

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.

• CWE-863Incorrect AuthorizationThe product performs an authorization check when an actor attempts to access a resource or perform an action, but it does not correctly perform the check.