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

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Summary

CVECVE-2026-49477
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-07-14 21:17:02 UTC
Updated2026-07-14 21:17:02 UTC
DescriptionSoup 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.

Risk And Classification

Primary CVSS: v3.1 7.5 HIGH from [email protected]

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Problem Types: CWE-400 | CWE-1333 | CWE-400 CWE-400: Uncontrolled Resource Consumption | CWE-1333 CWE-1333: Inefficient Regular Expression Complexity

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary7.5HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
3.1CNADECLARED7.5HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Facelessuser Soupsieve affected < 2.8.4 Not specified

References

ReferenceSourceLinkTags
github.com/facelessuser/soupsieve/security/advisories/GHSA-836r-79rf-4m37 [email protected] github.com
github.com/facelessuser/soupsieve/commit/eb4397618709186c109400448c6043b... [email protected] github.com
github.com/facelessuser/soupsieve/releases/tag/2.8.4 [email protected] github.com
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