---
id: CVE-2026-114134
aliases:
  - GHSA-cg8m-r9f2-5wm2
title: 'Black: GitHub Action installs unvalidated required-version from pyproject.toml'
summary: 'Black: GitHub Action installs unvalidated required-version from pyproject.toml'
severity: high
cwe:
  - CWE-829
vendor: black
product: black
ecosystem: pip
affected:
  - black < 26.10.1
patched:
  - black 26.10.1
published: '2026-10-22'
updated: '2026-10-22'
sourceUpdated: '2026-10-22T16:18:58Z'
source: GHSA
sourceUrl: 'https://github.com/advisories/GHSA-cg8m-r9f2-5wm2'
references:
  - url: 'https://github.com/psf/black/security/advisories/GHSA-cg8m-r9f2-5wm2'
  - url: 'https://github.com/psf/black/pull/5510'
  - url: >-
      https://github.com/psf/black/commit/ac1f71563aeccf73cf13ece00f231d9d6c66a514
  - url: 'https://github.com/psf/black/releases/tag/26.10.1'
  - url: 'https://github.com/advisories/GHSA-cg8m-r9f2-5wm2'
tags:
  - ghsa
  - pip
ingestedAt: '2026-10-22T22:00:50.257Z'
---

## Overview

### Summary

The GitHub Action bundled with Black can read the version from `tool.black.required-version` if `use_pyproject` is set to True. This version is not validated and therefore can be used to execute untrusted code in the context of a victim's repository.

### Details

This is similar to the previous CVE-2026-31900. The value in `tool.black.required-version` is accepted as the version to be installed by the action without validation.

### Proof of concept

Reproduction requires a victim to use Black's GitHub Action with `use_pyproject: true`. The attacker would then issue a PR to the victim's repository with `pyproject.toml` edited so that Black points to a malicious repository.

### Impact

This is a remote code execution vulnerability impacting users using the GitHub Action bundled with psf/black and using the `use_pyproject: true` setting.

## Affected packages

- `black < 26.10.1`

## Remediation

Upgrade to a patched release:

- `black 26.10.1`