CVE-2024-21503: Python Software Foundation Black

Medium severity, CVSS 5.3. EPSS: 1% chance of exploitation in the next 30 days.

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)

Published 2024-03-19. Last modified 2026-06-17.