CVE-2026-49477: Facelessuser Soup Sieve

High severity, CVSS 7.5. EPSS: 0.6% chance of exploitation in the next 30 days.

Soup Sieve is a CSS selector library designed to be used with Beautiful Soup 4. Prior to 2.8.4, the CSS selector parser in soupsieve contains a regular expression vulnerable to catastrophic backtracking when processing an attribute selector with an unterminated quoted value in soupsieve/css_parser.py, allowing an attacker who can supply untrusted CSS selector strings to soupsieve.compile() or Beautiful Soup .select() / .select_one() to cause CPU exhaustion and denial of service. This issue is fixed in version 2.8.4.

Affected products

• Facelessuser Soup Sieve: before 2.8.4 (fixed in 2.8.4)

Published 2026-07-14. Last modified 2026-07-28.