DOMPurify: Prototype Pollution to XSS Bypass via CUSTOM_ELEMENT_HANDLING Fallback

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Summary

CVECVE-2026-41238
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-04-23 16:16:26 UTC
Updated2026-04-23 18:16:29 UTC
DescriptionDOMPurify is a DOM-only cross-site scripting sanitizer for HTML, MathML, and SVG. Versions 3.0.1 through 3.3.3 are vulnerable to a prototype pollution-based XSS bypass. When an application uses `DOMPurify.sanitize()` with the default configuration (no `CUSTOM_ELEMENT_HANDLING` option), a prior prototype pollution gadget can inject permissive `tagNameCheck` and `attributeNameCheck` regex values into `Object.prototype`, causing DOMPurify to allow arbitrary custom elements with arbitrary attributes — including event handlers — through sanitization. Version 3.4.0 fixes the issue.

Risk And Classification

Primary CVSS: v3.1 6.9 MEDIUM from [email protected]

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

Problem Types: CWE-79 | CWE-1321 | CWE-79 CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') | CWE-1321 CWE-1321: Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution')

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary6.9MEDIUMCVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:H/I:L/A:N
3.1CNADECLARED6.9MEDIUMCVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:H/I:L/A:N

CVSS v3.1 Breakdown

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

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

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Cure53 DOMPurify affected >= 3.0.1, < 3.4.0 Not specified

References

ReferenceSourceLinkTags
github.com/cure53/DOMPurify/releases/tag/3.4.0 [email protected] github.com
github.com/cure53/DOMPurify/security/advisories/GHSA-v9jr-rg53-9pgp 134c704f-9b21-4f2e-91b3-4a467353bcc0 github.com
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