Medium [CVE-2026-49476] Denial of Service via crafted CSS selector string

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. An uncontrolled resource consumption vulnerability was found in the soupsieve Python package, a CSS selector library used by BeautifulSoup4.

A remote attacker could provide a crafted CSS selector string that causes excessive memory or CPU consumption, leading to a denial of service condition. It requires the application to accept untrusted CSS selectors supplied in one of the following sinks: * soupsieve.compile() * BeautifulSoup.select() * BeautifulSoup.select_one() This is an uncommon scenario.

Red Hat severity: Important — CVSS 5.9 (CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H). Weakness: CWE-770.

Affected products named by the advisory: Red Hat Hardened Images; Red Hat OpenShift AI 3.4; Exploit Intelligence; Lightspeed Core; and 9 more.