CVE-2026-49477
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…
Does this matter?
High impact if exploited, but EPSS currently rates exploitation as unlikely (0.52%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit.
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.
- CVSS 3.1
- 7.5 HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- EPSS
- 0.52% probability · 43th percentile
- CISA KEV
- Not listed
- Weakness
- CWE-400, CWE-1333
- Affected
- facelessuser/soup sieve
- Source
- security-advisories@github.com
References
- https://github.com/facelessuser/soupsieve/commit/eb4397618709186c109400448c6043b728217dc3Patch
- https://github.com/facelessuser/soupsieve/releases/tag/2.8.4Release Notes
- https://github.com/facelessuser/soupsieve/security/advisories/GHSA-836r-79rf-4m37Exploit, Vendor Advisory
- https://github.com/facelessuser/soupsieve/security/advisories/GHSA-836r-79rf-4m37Exploit, Vendor Advisory
Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.