by Kastro
Paper/Archive/CVE-2026-31900

CVE-2026-31900

psf black — Black's vulnerable version parsing leads to RCE in GitHub Action

EPSS 0.5%CVSS 9.8
critical.is priorityof 100
38
CVSS 9.8 (NVD)9.8 / 10 × 3029.4Not in CISA KEV+300.0EPSS percentile 42.1.421 × 208.4No public exploit+100.0SSVC exploitation: none+100.0
Description · from the CVE record

Black is the uncompromising Python code formatter. 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. Version 26.3.0 fixes this vulnerability.

Affected

ProductAffectedFixed inSource
black< 26.3.0–CNA

Scores by source

NVD9.8CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
GitHub_M (CNA)8.7CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
CISA ADPSSVCExploitation: none · Automatable: no · Technical impact: total

References

refgithub.com/psf/black/security/advisories/GHSA-v53h-f6m7-xcgmrefgithub.com/psf/black/commit/0a2560b981364dde4c8cf8ce9d164c40669a8611