Vulnerability Report

CVE-2026-31900

Title: Arbitrary Code Execution in Black GitHub action via pyproject.toml

Input Validation Error

Proof Of Concept

PoC Available for CVE-2026-31900

CWE Category CWE-20

Published Date Mar 11, 2026

Modified Date Mar 16, 2026

Exploit Status Available

Score 8.7 CVSS v4.0

Exploit Probability (EPSS)

0.46%

Vulnerability Summary

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.

Impacted Vendors

python 1

Reference Links

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

CVSS v4.0

Source Entity [email protected]

Severity HIGH

8.7

Attack Vector

NETWORK

Complexity

LOW

Privileges

N/A

Interaction

NONE

Confidentiality

N/A

Integrity

N/A

Availability

N/A

Scope

N/A

RAW VECTOR

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:X/V:X/RE:X/U:X

CVSS v3.1

Source Entity [email protected]

Severity CRITICAL

9.8