CVE-2026-31900

Name	CVE-2026-31900
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.
Source	CVE (at NVD; CERT, ENISA, LWN, oss-sec, fulldisc, Debian ELTS, Red Hat, Ubuntu, Gentoo, SUSE bugzilla/CVE, GitHub advisories/code/issues, web search, more)

Vulnerable and fixed packages

The table below lists information on source packages.

Source Package	Release	Version	Status
black (PTS)	bullseye	20.8b1-4	vulnerable
	bookworm	23.1.0-1	vulnerable
	trixie	25.1.0-3	vulnerable
	forky	25.12.0-2	vulnerable
	sid	26.1.0-1	vulnerable

The information below is based on the following data on fixed versions.

Package	Type	Release	Fixed Version	Urgency	Origin	Debian Bugs
black	source	(unstable)	(unfixed)	unimportant

Notes

https://github.com/psf/black/security/advisories/GHSA-v53h-f6m7-xcgm
Fixed by: https://github.com/psf/black/commit/0a2560b981364dde4c8cf8ce9d164c40669a8611 (26.3.0)
GitHub action code from action/main.py not provided in the Debian built binay packages