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Vulnerability record · CVE-2026-31900 · published 11 March 2026

CVE-2026-31900: Python black improper input validation vulnerability

Python · Black

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.

8.7 CVSS 4.0 High EPSS 0.64% · top 51.6% CWE-20 · Improper input validation
8.7CVSS 4.0 base score
0.64%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
2References
17 Jun 2026Last modified by NVD

Description

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.

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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://github.com/psf/black/commit/0a2560b981364dde4c8cf8ce9d164c40669a8611 Patch
https://github.com/psf/black/security/advisories/GHSA-v53h-f6m7-xcgm MitigationVendor Advisory

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Source: NIST National Vulnerability Database (record CVE-2026-31900), CISA KEV, FIRST EPSS (scores of 2026-09-27). This page is refreshed as NVD updates the record.