How severe is CVE-2026-31900?

CVE-2026-31900 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2026-31900 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (37th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-31900?

CVE-2026-31900 affects Python Black. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-31900?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.

Does CVE-2026-31900 have an EU (EUVD) identifier?

Yes. CVE-2026-31900 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-11315.

When was CVE-2026-31900 published?

CVE-2026-31900 was published on 2026-03-11 and last updated on 2026-06-17.

CVE-2026-31900

CVE-2026-31900 is a critical-severity vulnerability in Python Black with a CVSS 3.x base score of 9.8. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-20.

Key facts

Severity: Critical (CVSS 3.x base score 9.8)
CVSS v4: 8.7
EPSS exploit prediction: 0% (37th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-11315
Weakness: CWE-20
Affected product: Python Black
Published: 2026-03-11
Last modified: 2026-06-17

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.

Frequently asked questions

What is CVE-2026-31900?: 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.
How severe is CVE-2026-31900?: CVE-2026-31900 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2026-31900 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (37th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-31900?: CVE-2026-31900 affects Python Black. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-31900?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.
Does CVE-2026-31900 have an EU (EUVD) identifier?: Yes. CVE-2026-31900 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-11315.
When was CVE-2026-31900 published?: CVE-2026-31900 was published on 2026-03-11 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:python:black:*:*:*:*:*:*:*:*

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