CVE-2026-49477

Analyzed Analyzed - Analysis Complete

Soup Sieve CSS Selector Regex Denial of Service

Publication date: 2026-07-14

Last updated on: 2026-07-28

Assigner: GitHub, Inc.

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 Scores

EPSS Scores

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Meta Information

Published

2026-07-14

Last Modified

2026-07-28

Generated

2026-08-04

AI Q&A

2026-07-15

EPSS Evaluated

2026-08-02

NVD

CVE-2026-49477

Affected Vendors & Products

Vendor	Product	Version / Range
facelessuser	soup_sieve	to 2.8.4 (exc)

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-1333	The product uses a regular expression with an inefficient, possibly exponential worst-case computational complexity that consumes excessive CPU cycles.
CWE-400	The product does not properly control the allocation and maintenance of a limited resource.

Attack-Flow Graph

Executive Summary

Soup Sieve is a CSS selector library for Beautiful Soup 4. The vulnerability exists in versions before 2.8.4 where a regular expression in the CSS selector parser can be exploited by an attacker providing a malicious CSS selector with an unterminated quoted value. This causes catastrophic backtracking, leading to CPU exhaustion and denial of service.

Detection Guidance

This vulnerability can be detected by checking the version of Soup Sieve in use. If your system uses Soup Sieve version prior to 2.8.4, it is vulnerable. Run: pip show soupsieve to check the installed version.

Impact Analysis

If you use a vulnerable version of Soup Sieve, an attacker could send a specially crafted CSS selector string to cause high CPU usage, potentially crashing your application or server. This could disrupt services relying on Beautiful Soup or Soup Sieve for parsing.

Compliance Impact

This vulnerability could lead to denial of service, impacting availability of services. For GDPR, availability is a key principle, so prolonged outages may raise compliance concerns. HIPAA also requires availability of protected health information systems, making this a potential compliance risk if exploited.

Mitigation Strategies

Upgrade Soup Sieve to version 2.8.4 or later immediately. Use pip install --upgrade soupsieve to update. If using Beautiful Soup, ensure it depends on a patched version of Soup Sieve.

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