CVE-2026-31900Network attack vector

Code execution via direct URL version reference

Published Mar 11, 2026 · Updated Mar 11, 2026

Improper input validation in the Black GitHub Action before 26.3.0 allows attackers to execute code via a crafted pull request. With use_pyproject enabled, the Action's version parser accepts a direct URL after the Black package name and passes the resulting requirement to pip. A pull request must modify pyproject.toml, after which malicious package code runs with the secrets and permissions available to the workflow.

CVSS severity8.7
High
EPSS probability0.46%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper input validation in the Black GitHub Action before 26.3.0 allows attackers to execute code via a crafted pull request. With use_pyproject enabled, the Action's version parser accepts a direct URL after the Black package name and passes the resulting requirement to pip. A pull request must modify pyproject.toml, after which malicious package code runs with the secrets and permissions available to the workflow.

The record

CVE
CVE-2026-31900
Published
Mar 11, 2026
Updated
Mar 11, 2026
Vendor
Python Software Foundation
Product
Black
Classifications
CWE-20
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Mar 11, 2026CVE publishedPublication date reported by the CVE source.
  2. Mar 11, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 26.3.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Python Software Foundation · Blackversion=< 26.3.0

Published CVSS scores

8.7GitHub, Inc.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
9.8NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-20Improper Input Validation

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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