Soup Sieve: Quadratic-time denial of service when matching `:has()`

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-126189
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-11-12 17:17:32 UTC
Updated2026-11-12 19:09:06 UTC
DescriptionSoup Sieve is a CSS selector library designed to be used with Beautiful Soup 4. Prior to 4.0.1, Soup Sieve repeatedly searches descendant subtrees for each candidate evaluated by :has() and repeatedly reevaluates a parent containing :has(> ...) for each child, causing quadratic matching on deeply nested or wide attacker-influenced HTML or XML. Applications using ordinary fixed selectors through select(), select_one(), or Beautiful Soup CSS APIs against untrusted documents can have a worker occupied for seconds or minutes, while applications that process only trusted documents are not affected. Selectors compiled with NOCACHE continue to use the old uncached behavior. This issue is fixed in version 4.0.1.

Risk And Classification

Primary CVSS: v3.1 5.3 MEDIUM from [email protected]

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

Problem Types: CWE-407 | CWE-407 CWE-407: Inefficient Algorithmic Complexity

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary5.3MEDIUMCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
3.1CNADECLARED5.3MEDIUMCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

CVSS v3.1 Breakdown

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

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

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Facelessuser Soupsieve affected < 4.0.1 Not specified

References

ReferenceSourceLinkTags
github.com/facelessuser/soupsieve/security/advisories/GHSA-8jvp-3x96-xpqw [email protected] github.com
github.com/facelessuser/soupsieve/commit/305fbf6b8c1f6ff05fec55d1e5bb28d... [email protected] github.com
github.com/facelessuser/soupsieve/releases/tag/4.0.1 [email protected] github.com
github.com/facelessuser/soupsieve/commit/0469c148f5501ec2127e0d65b77c2a1... [email protected] github.com
github.com/facelessuser/soupsieve/pull/352 [email protected] github.com
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