Description
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
References4
- github.com/facelessuser/soupsieve/security/advisories/GHSA-836r… ExploitVendor Advisory
- github.com/facelessuser/soupsieve/security/advisories/GHSA-836r… ExploitVendor Advisory
- github.com/facelessuser/soupsieve/commit/eb4397618709186c109400… Patch
- github.com/facelessuser/soupsieve/releases/tag/2.8.4 Release Notes
Metrics
- CVSS 3.1
-
7.5
HIGH
Score source: CNA
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H - EPSS — exploit probability
- 1% percentile: 51 · as of 15 November 2026
- CWE
- CWE-400CWE-1333
Could this be exploited in your environment?
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