Medium severity · published Oct 6, 2026
CVE-2026-103620
Missing authorization in GitHub Enterprise Server allowed repository writers to replace default branches via GraphQL
6.5
CVSS
0.5%
EPSS
No
On KEV
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.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N
Attack vector
Network
Complexity
Low
Privileges
Low
User interaction
None
Confidentiality
None
Integrity
High
Availability
None
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.5% · higher than 43% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
ES
Enterprise Server · GitHub
3.18.0 before 3.18.*; 3.19.0 before 3.19.*; 3.20.0 before 3.20.*; 3.21.0 before 3.21.*; 3.22.0 before 3.22.* · source: vendor, NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-103620
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-103620
release-notes
https://docs.github.com/en/enterprise-server@3.18/admin/release-notes#3.18.16
release-notes
https://docs.github.com/en/enterprise-server@3.19/admin/release-notes#3.19.13
release-notes
https://docs.github.com/en/enterprise-server@3.20/admin/release-notes#3.20.9
release-notes
https://docs.github.com/en/enterprise-server@3.21/admin/release-notes#3.21.7
release-notes
https://docs.github.com/en/enterprise-server@3.22/admin/release-notes#3.22.2
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