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CVE-2026-31900

Python Black vulnerability

9.8 CRITICALEPSS 0.66%
  1. Published11 Mar 2026

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.

CVSS 3.1 breakdown

Attack vectorNetwork
Attack complexityLow
Privileges requiredNone
User interactionNone
ScopeUnchanged
ConfidentialityHigh
IntegrityHigh
AvailabilityHigh
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Affected products

Python Black< 26.3.0

Remediation

Fixed in
Python Black≥ 26.3.0

References

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Frequently asked

Is CVE-2026-31900 being actively exploited?

CVE-2026-31900 is not in the CISA KEV catalog. Its EPSS exploit probability is 0.66%.

How severe is CVE-2026-31900?

CVE-2026-31900 has a CVSS 3.1 base score of 9.8, rated critical. EPSS estimates a 0.66% probability of exploitation.

Which products are affected by CVE-2026-31900?

Affected products include Python Black.

How do I fix CVE-2026-31900?

Upgrade affected software to a fixed version, for example Python Black 26.3.0 or later, then confirm no affected versions remain in your inventory.

How Secuno handles this

Secuno correlates vulnerabilities like CVE-2026-31900 against the real software inventory on every managed device, every day. Rather than a static severity, each match is scored in context: exploit availability, EPSS, the asset's exposure, and business criticality decide where it lands in the queue. If an affected version is present anywhere across your portfolio, it surfaces automatically with a prioritised remediation path.

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Data from the NVD, CISA KEV catalog and FIRST EPSS. CVSS 3.1 base score shown where available.