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 allocates unbounded memory when compiling large comma-separated selector lists, allowing an attacker who can supply a crafted selector string to soupsieve.compile() or Beautiful Soup .select() / .select_one() to allocate hundreds of megabytes of heap memory from a relatively small input and cause 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-2wc2… ExploitVendor Advisory
- github.com/facelessuser/soupsieve/security/advisories/GHSA-2wc2… ExploitVendor Advisory
- github.com/facelessuser/soupsieve/commit/28108ab805818c832d9568… 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-770
Could this be exploited in your environment?
A patch closes the known hole. A penetration test shows what an attacker can still reach — with proof.