What’s Vulnerable › Vulnerabilities

CVE-2024-21503

• Severity: medium (CVSS 5.3 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 1.0% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2024-03-19 · updated 2026-06-17
• Weakness: CWE-1333

Description

Versions of the package black before 24.3.0 are vulnerable to Regular Expression Denial of Service (ReDoS) via the lines_with_leading_tabs_expanded function in the strings.py file. An attacker could exploit this vulnerability by crafting a malicious input that causes a denial of service. Exploiting this vulnerability is possible when running Black on untrusted input, or if you habitually put thousands of leading tab characters in your docstrings.

Affected products

• Python Software Foundation Black: before 24.3.0 — fixed in 24.3.0

How to fix

Upgrade to a fixed version: Python Software Foundation Black 24.3.0. Check the vendor advisory for mitigations.

References

• https://github.com/psf/black/commit/f00093672628d212b8965a8993cee8bedf5fe9b8
• https://github.com/psf/black/releases/tag/24.3.0
• https://security.snyk.io/vuln/SNYK-PYTHON-BLACK-6256273
• https://github.com/psf/black/commit/f00093672628d212b8965a8993cee8bedf5fe9b8
• https://github.com/psf/black/releases/tag/24.3.0
• https://security.snyk.io/vuln/SNYK-PYTHON-BLACK-6256273

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