CVE-2026-1999

MEDIUM

GitHub Enterprise Server - Auth Bypass

Title source: llm
STIX 2.1

Exploitation Summary

EIP tracks 3 public exploits for CVE-2026-1999. PoCs published by manoelprovider20-lgtm, SecureWithUmer, jwde.

AI-analyzed exploit summary The repository contains only a README.md file with a vague reference to 'authz test (CVE-2026-1999 siblings)', providing no technical details, exploit code, or vulnerability analysis. It appears to be an incomplete or placeholder repository.

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.

Exploits (3)

nomisec STUB
by manoelprovider20-lgtm · poc
https://github.com/manoelprovider20-lgtm/merge-authz-test

The repository contains only a README.md file with a vague reference to 'authz test (CVE-2026-1999 siblings)', providing no technical details, exploit code, or vulnerability analysis. It appears to be an incomplete or placeholder repository.

Classification
Stub 95%
Attack Type
Other
Complexity
Trivial
Reliability
Theoretical
Target: unspecified
No auth needed
mistral-large-3 · analyzed Jul 18, 2026 Full analysis →
github STUB
by SecureWithUmer · c++poc
https://github.com/SecureWithUmer/CVE-2026-PoCs/tree/main/2026/CVE-2026-1999

The repository contains minimal placeholder content with no functional exploit code, technical details, or vulnerability analysis. It includes a GitHub Actions workflow file with a trivial echo command and a README with only a reference to the NVD entry for CVE-2026-1999.

Classification
Stub 95%
Attack Type
Other
Complexity
Trivial
Reliability
Theoretical
Target: unknown
No auth needed
mistral-large-3 · analyzed Jul 08, 2026 Full analysis →
nomisec STUB
by jwde · poc
https://github.com/jwde/automerge-test

The repository contains minimal content with a placeholder README and a basic GitHub Actions workflow file. There is no functional exploit code or technical details related to CVE-2026-1999.

Classification
Stub 90%
Attack Type
Other
Complexity
Trivial
Reliability
Theoretical
Target: unknown
No auth needed
mistral-large-3 · analyzed Mar 16, 2026 Full analysis →

Scores

CVSS v3 6.5
EPSS 0.0029
EPSS Percentile 21.6%
Attack Vector NETWORK
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N

CISA SSVC

Vulnrichment
Exploitation none
Automatable no
Technical Impact partial

Details

CWE
CWE-863
Status published
Products (4)
GitHub/Enterprise Server 3.17.0 - 3.17.11
GitHub/Enterprise Server 3.18.0 - 3.18.5
GitHub/Enterprise Server 3.19.0 - 3.19.2
github/enterprise_server < 3.17.11
Published Feb 18, 2026
Tracked Since Feb 19, 2026