CVE-2026-114134 Black: GitHub Action installs unvalidated required-version from pyproject.toml

Description

Black is the uncompromising Python code formatter. Prior to 26.10.1, the Black GitHub Action with use_pyproject: true accepts tool.black.required-version from pyproject.toml without validating that it is a released Black version specifier. An attacker who can submit a pull request can change that field to a direct reference to attacker-controlled code, causing the workflow to install and execute the code in the victim repository's GitHub Actions context. This issue is fixed in version 26.10.1.

Exploitable remotely over the network, with an ordinary account and without any user action; an attacker can seriously compromise confidentiality, integrity or availability.

Attack vector

Network

Attack complexity

Low

Attack requirements

None

Privileges required

Low

Interaction

None

Confidentiality

High

Integrity

High

Availability

High

Confidentiality of other systems

None

Integrity of other systems

None

Availability of other systems

None

Affected products and versions