CVE-2021-22861: Improper access control in GitHub Enterprise Server leading to unauthorized write access to forkable repositories

Severity: medium (CVSS 6.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 1.0% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2021-03-03 · updated 2026-06-17
Weakness: CWE-285

Description

An improper access control vulnerability was identified in GitHub Enterprise Server that allowed authenticated users of the instance to gain write access to unauthorized repositories via specifically crafted pull requests and REST API requests. An attacker would need to be able to fork the targeted repository, a setting that is disabled by default for organization owned private repositories. Branch protections such as required pull request reviews or status checks would prevent unauthorized commits from being merged without further review or validation. This vulnerability affected all versions of GitHub Enterprise Server since 2.4.21 and was fixed in versions 2.20.24, 2.21.15, 2.22.7 and 3.0.1. This vulnerability was reported via the GitHub Bug Bounty program.

Affected products

Github: from 2.4.21 before 2.20.24; from 2.21.0 before 2.21.15; from 2.22.0 before 2.22.7; from 3.0.0 before 3.0.1 — fixed in 2.20.24, 2.21.15, 2.22.7, 3.0.1

How to fix

Upgrade to a fixed version: Github 2.20.24, 2.21.15, 2.22.7, 3.0.1. Check the vendor advisory for mitigations.

References

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