Loofah: CSS url() sanitization bypass via escaped parentheses

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-126207
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-11-12 21:17:21 UTC
Updated2026-11-12 22:09:39 UTC
DescriptionLoofah is a general library for manipulating and transforming HTML/XML documents and fragments, built on top of Nokogiri. Prior to 2.25.3, Loofah::HTML5::Scrub.scrub_css checks only the first parse of a style attribute, then rebuilds CSS with identifier escapes decoded so escaped parentheses, property names, comments, or quotes can become a live url() without a second safety check. An attacker can use list-style to make a viewer's browser request an attacker-chosen URL when content renders, or cursor to make the request on hover. The request can disclose the viewer's IP address, user agent, access timing, and access to internal-network hosts, but no script survives sanitization and the attacker cannot read the response. This issue is fixed in version 2.25.3.

Risk And Classification

Primary CVSS: v3.1 4.7 MEDIUM from [email protected]

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

Problem Types: CWE-180 | CWE-184 | CWE-180 CWE-180: Incorrect Behavior Order: Validate Before Canonicalize | CWE-184 CWE-184: Incomplete List of Disallowed Inputs

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary4.7MEDIUMCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:N/A:N
3.1CNADECLARED4.7MEDIUMCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:N/A:N

CVSS v3.1 Breakdown

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

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

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Flavorjones Loofah affected < 2.25.3 Not specified

References

ReferenceSourceLinkTags
github.com/flavorjones/loofah/pull/324 [email protected] github.com
github.com/flavorjones/loofah/security/advisories/GHSA-m3x9-938q-5767 [email protected] github.com
github.com/flavorjones/loofah/releases/tag/v2.25.3 [email protected] github.com
github.com/flavorjones/loofah/commit/b198a36e44c9c5408163ac50787825e8ca0... [email protected] github.com
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