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CVE-2026-31900

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

Published: Mar 11, 2026Updated: Mar 16, 2026 Sources: CVE List NVD GHSACWE-20
NVD MITRE
9.8CVSSCRITICAL
EPSS Score
0.5%
Top 63.7%
CISA KEV
Not in KEV
Exploits
No Known Exploits
Remediation
Patch Available

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 Vector Breakdown

AV:NAC:LPR:NUI:NS:UC:HI:HA:H
Exploitability
AV:NAttack Vector
Network
AC:LAttack Complexity
Low
PR:NPrivileges Required
None
UI:NUser Interaction
None
Scope
S:UScope
Unchanged
Impact
C:HConfidentiality
High
I:HIntegrity
High
A:HAvailability
High
Open in CVSS calculator →

Weaknesses

CWE-20NVD-CWE-noinfo

Affected Products

blackpythonOSS Libraries
psf/blackGitHub Actions
SaaS
DevTools & CI / ci-cd
blackpsf
Library
OSS Libraries / generic-library
pythonoss-projectUSOSS Libraries
github actionscommercialUSDevTools & CIaka github actions
psfoss-projectOSS Librariesaka psf

Attack Graph

Products CVE Techniques Tactics

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Exploitability

Official Patch Available
Workaround Available

MITRE ATT&CK

1 technique
Initial Access
View detailed technique mapping

References

https://github.com/psf/black/commit/0a2560b981364dde4c8cf8ce9d164c40669a8611
github.com
https://github.com/psf/black/security/advisories/GHSA-v53h-f6m7-xcgm
github.com
https://nvd.nist.gov/vuln/detail/CVE-2026-31900
nvd.nist.gov
and 1 more references View all →

Timeline

Published
Mar 11, 2026
Last Updated
Mar 16, 2026

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