CVE-2026-86000

Vulnerability Description

Soup Sieve is a CSS selector library designed to be used with Beautiful Soup 4. Prior to 2.9, the selector parser in src/soupsieve/css_parser.py defines IDENTIFIER with adjacent quantified groups over overlapping character classes, and VALUE embeds IDENTIFIER for attribute selectors. When an attacker-controlled selector contains a long identifier or unquoted attribute-value run followed by input that makes the overall match fail, the regular expression engine explores quadratically many splits between the overlapping groups. User-controlled selectors can reach this path through soupsieve.compile(), soupsieve.select(), or BeautifulSoup.select(), while applications using only hard-coded selectors are unaffected. The resulting CPU consumption can hold the Python GIL, exhaust application workers, and stall a service; successful plain identifier matches are linear, and the issue does not cause memory corruption or code execution. The issue is fixed in version 2.9.

CVSS Score

Related Weaknesses (CWE)

References

• https://github.com/facelessuser/soupsieve/commit/ce44e4996e6632871c18cdd7a7fb641
• https://github.com/facelessuser/soupsieve/releases/tag/2.9
• https://github.com/facelessuser/soupsieve/security/advisories/GHSA-gjv8-xp57-g29
• https://github.com/facelessuser/soupsieve/security/advisories/GHSA-gjv8-xp57-g29