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CVE-2026-103620— Missing authorization in GitHub Enterprise Server allowed repository writers to replace default branches via GraphQL

Quick assessment

Affected
GitHub Enterprise Server
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

在 GitHub Enterprise Server 中发现了一个缺失的身份验证漏洞，该漏洞允许具有写入权限的仓库协作者通过 GraphQL API 删除当前的默认分支，从而导致攻击者控制的分支成为新的默认分支。在要求拉取请求（PR）审查但未限制分支删除的仓库中，此漏洞绕过了审查要求，使得新生成的克隆仓库以及默认分支的 API 请求使用攻击者控制的代码内容。此漏洞影响了支持的 GitHub Enterprise Server 3.18、3.19、3.20、3.21 和 3.22 系列版本，并在版本 3.18.16、

CVSS 6.0 · Medium
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I. Basic Information for CVE-2026-103620

Vulnerability Information
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Vulnerability Title
Missing authorization in GitHub Enterprise Server allowed repository writers to replace default branches via GraphQL
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N
Source: CVE Program / CVE List V5
Vulnerability Type
授权机制缺失
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
GitHub Enterprise Server 3.18.0 ~ 3.18.* -

II. Public POCs for CVE-2026-103620

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III. Intelligence Information for CVE-2026-103620

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Other References for CVE-2026-103620 (5)

IV. Related Vulnerabilities

Same product: Enterprise Server
Same vendor: GitHub
Same weakness: CWE-862

V. Comments for CVE-2026-103620

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