CVE-2026-49477CWE-1333CWE-400

Soup Sieve: Regular Expression Denial of Service (ReDoS) in soupsieve Selector Parser

High · published July 14, 2026

CVSS v3.1
7.5
EPSS
1%
Percentile
50.2
In the wild
Unconfirmed
What it is

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.

The record
Technical detail
CVSS v3.1
7.5 · HIGH
Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
CVSS v4.0
Not supplied
EPSS
0.00644 · 50.2th percentile
Weaknesses
CWE-1333 · Inefficient Regular Expression Complexity; CWE-400 · Uncontrolled Resource Consumption
Published
2026-07-14T20:51Z
EPSS history
Timeline
  • 14 JUL 20:51Z
    Soup Sieve: Regular Expression Denial of Service (ReDoS) in soupsieve Selector Parser
    cvelistv5