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CVE-2026-103620

Missing authorization in GitHub Enterprise Server allowed repository writers to replace default branches via GraphQL

MEDIUM
6.5
CVSS Score
Published: October 6, 2026 at 06:56 PM UTC
Updated: October 20, 2026 at 07:33 PM UTC
1 product affected across 1 vendorGitHub Enterprise Server

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Severity
MEDIUM6.5
Exploit prediction
EPSS 0.5%
SSVC
No known exploit

Description

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.

Affected

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

GitHub Enterprise Server· GitHubgithub-action
95%
3.18.0 ≤ v < 3.18.163.19.0 ≤ v < 3.19.133.20.0 ≤ v < 3.20.93.21.0 ≤ v < 3.21.73.22.0 ≤ v < 3.22.23.18.03.19.03.20.03.21.03.22.0

References (5)

Release NotesVendor Advisory
Source: cverecord
https://docs.github.com/en/[email protected]/admin/release-notes#3.18.16
Release NotesVendor Advisory
Source: cverecord
https://docs.github.com/en/[email protected]/admin/release-notes#3.19.13
Release NotesVendor Advisory
Source: cverecord
https://docs.github.com/en/[email protected]/admin/release-notes#3.20.9
Release NotesVendor Advisory
Source: cverecord
https://docs.github.com/en/[email protected]/admin/release-notes#3.21.7
Release NotesVendor Advisory
Source: cverecord
https://docs.github.com/en/[email protected]/admin/release-notes#3.22.2

SSVC — Action Prioritization

SSVCNo known exploitNot automatablePartial impact

SSVC signals action urgency (what to patch first), separate from CVSS which measures severity.

CVSS

6.5MEDIUM[email protected]
Attack Vector
NETWORK
Complexity
LOW
Privileges
LOW
User Interaction
NONE
Scope
UNCHANGED
Confidentiality
NONE
Integrity
HIGH
Availability
NONE
Vector?

Quick Info

StatusANALYZED
CWE
CWE-862

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