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CVE-2026-31900— Black's vulnerable version parsing leads to RCE in GitHub Action

Quick assessment

Affected
psf black
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Black是Python Software Foundation开源的一个 Python 代码格式化程序。 Black 26.3.0之前版本存在输入验证错误漏洞，该漏洞源于恶意拉取请求可配置使用恶意仓库URL，可能导致任意代码执行。

AI Predicted 9.8 Difficulty: Easy EPSS 0.46% · P38
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I. Basic Information for CVE-2026-31900

Vulnerability Information
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Vulnerability Title
Black's vulnerable version parsing leads to RCE in GitHub Action
Source: CVE Program / CVE List V5
Vulnerability 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 Program / CVE List V5
CVSS Information
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
Source: CVE Program / CVE List V5
Vulnerability Type
输入验证不恰当
Source: CVE Program / CVE List V5
Vulnerability Title
Black 输入验证错误漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Black是Python Software Foundation开源的一个 Python 代码格式化程序。 Black 26.3.0之前版本存在输入验证错误漏洞，该漏洞源于恶意拉取请求可配置使用恶意仓库URL，可能导致任意代码执行。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
psf black < 26.3.0 -

II. Public POCs for CVE-2026-31900

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III. Intelligence Information for CVE-2026-31900

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Patches & Fixes for CVE-2026-31900 (1)

Vendor Advisories for CVE-2026-31900 (1)

IV. Related Vulnerabilities

Same product: black
Same vendor: psf
Same weakness: CWE-20

V. Comments for CVE-2026-31900

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