Improper input validation in Psf Black
CVE-2026-31900
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.
Vulnerability class: Drupalgeddon 2 (CVE-2018-7600)
EPSS: 0.005 (37.5th percentile) — read the EPSS interpretation.
CVSS v3 metric
CVSS v3 base score 9.8 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.
Affected products
- Psf Black — versions < 26.3.0
- Python Black
Weakness classification (CWE)
Public proof-of-concept exploits
References
- security-advisories@github.com (x_refsource_CONFIRM, Mitigation, Vendor Advisory)
- security-advisories@github.com (Patch, x_refsource_MISC)
Frequently asked questions
- What is CVE-2026-31900?
- CVE-2026-31900 is a critical-severity vulnerability in Psf Black, classified under Improper Input Validation. CVSS score: 9.8/10. Published 2026-03-11.
- How severe is CVE-2026-31900?
- Critical severity. CVSS v3 base score is 9.8 out of 10.
- Is CVE-2026-31900 known to be exploited?
- 1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.