GitHub Advisoryadvisory · GitHub Actions
GHSA-v53h-f6m7-xcgm Black's vulnerable version parsing leads to RCE in GitHub Action
HIGH
Official page ↗
- Aliases
- CVE-2026-31900
- Ecosystem
- GitHub Actions
- Packages
- psf/black
- Severity
- High
- CVSS vector
- CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
- Weaknesses
- CWE-20
- Reviewed
- 2026-03-07
Affected packages
• GitHub Actions psf/black: < 26.3.0 → fixed in 26.3.0
Description
Impact
Black provides a GitHub action for formatting code. This action supports an option, `use_pyproject: true`, for reading the version of Black to use from the repository `pyproject.toml`. A malicious pull request could edit pyproject.toml to use a direct URL reference to a malicious repository. This could lead to arbitrary code execution in the context of the GitHub Action. Attackers could then gain access to secrets or permissions available in the context of the action.
Patches
Version 26.3.0 fixes this vulnerability by tightening the validation of the `version` field. Users who use the GitHub Action as `psf/black@stable` will automatically pick up this update.
Workarounds
Do not use the `use_pyproject: true` option in the psf/black GitHub Action.
Related
Alias · CVE (1)
- CVE-2026-31900 Black is the uncompromising Python code formatter. vulnerability
Weakness · CWE (1)
- CWE-20 Improper Input Validation weakness