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TI-2026-68589 Aliases CVE-2026-103620GHSA-mj9w-xm4p-h2mp

GitHub Enterprise Server lets writers replace default branches

Priority LOW 27CWE-862Published · Updated

Key facts

Attack vector
Network
Privileges required
Low
User interaction
None
Attack complexity
Low
Attack requirements
Present
Impact type
Security bypass
Confidentiality · integrity · availability
None · High · None
Fix status
No fix listed

Attack profile from CVSS 4.0 · CNA. Fix status from CNA. Impact type from CWE-862.

Summary

GitHub Enterprise Server releases in the 3.18, 3.19, 3.20, 3.21 and 3.22 series are affected. A missing authorization check (CWE-862) lets a repository collaborator with write access delete the current default branch through the GraphQL API, so an attacker-controlled branch becomes the default. In repositories that require pull request review but do not restrict branch deletion, this bypasses the review requirement and makes fresh clones and default branch API requests use attacker-controlled content.

Written with Claude Haiku 5.5 from the sources below · 2026-10-29

Description from the CNA

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.

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.00499 43rd percentileScored 2026-11-07
Fix No fix listed No fixed version in the sources yet

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
None
Automatable
No
Technical impact
Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

VendorProductAffected versionsFixed inStatusSource
GitHubEnterprise Server3.18.0 and later; 3.19.0 and later; 3.20.0 and later; 3.21.0 and later; 3.22.0 and later—No fix listedCNA
  • Enterprise Server VendorGitHub Affected 3.18.0 and later; 3.19.0 and later; 3.20.0 and later; 3.21.0 and later; 3.22.0 and later Fixed in — No fix listed CNA

CPE configurations NVD · 1

CPEVersionsRoleVendor
cpe:2.3:a:github:enterprise_server:*:*:*:*:*:*:*:*3.18.0 to before 3.18.16; 3.19.0 to before 3.19.13; 3.20.0 to before 3.20.9; 3.21.0 to before 3.21.7; 3.22.0 to before 3.22.2VulnerableGitHub
  • cpe:2.3:a:github:enterprise_server:*:*:*:*:*:*:*:* Versions 3.18.0 to before 3.18.16; 3.19.0 to before 3.19.13; 3.20.0 to before 3.20.9; 3.21.0 to before 3.21.7; 3.22.0 to before 3.22.2 Vulnerable ·GitHub

Remediation

Upgrade GitHub Enterprise Server to 3.18.16, 3.19.13, 3.20.9, 3.21.7 or 3.22.2, matching the release series in use.

Written with Claude Haiku 5.5 from the sources below · 2026-10-29

Timeline

  1. 2026-10-06 Threatist record created from CVE-2026-103620
  2. 2026-10-07 Alias added: GHSA-mj9w-xm4p-h2mp
  3. 2026-10-07 CISA SSVC decision points changed
  4. 2026-10-07 Priority changed: MEDIUM → LOW
  5. 2026-10-21 CVSS score added · NVD

References

Advisory 5

  • TI-2024-04632 An authentication bypass vulnerability was present in the GitHub Enterprise Server (GHES)… CVSS 4.0CRITICAL 10.0
  • TI-2024-00181 Unsafe Reflection in Github Enterprise Server leading to Command Injection CVSS 3.1CRITICAL 9.8
  • TI-2024-00466 Privilege Escalation by Code Injection in the Management Console in GitHub Enterprise Server CVSS 3.1HIGH 8.8
  • TI-2026-03340 Remote code execution via git push option injection in GitHub Enterprise Server CVSS 4.0HIGH 8.7
  • TI-2024-08804 Improper signature verification in GitHub Enterprise Server CVSS 4.0CRITICAL 9.5
  • TI-2026-08177 Server-side request forgery in GitHub Enterprise Server CVSS 4.0CRITICAL 9.2
See all 125 →

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences