Black is the uncompromising Python code formatter. Prior to 26.3.1, Black writes a cache file, the name of which is computed from various formatting options. The value of the --python-cell-magics option was placed in the filename without sanitization, which allowed an attacker who controls the value of this argument to write cache files to arbitrary file system locations. Fixed in Black 26.3.1.
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black
Vendor: python
Actively Exploited
0
CISA KEV List
PoC / Exploits
1
Code Available
Total RCEs
0
Remote Access
Total CVEs
7
Total Indexed
Avg. EPSS
0.52%
Exploit Prob.
Security Vulnerability Index
Page 1 / 1
8.7
CVSS
Severity: HIGH
8.7
CVSS
CVE-2026-31900
Exploit Found
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.
Severity: HIGH