What’s Vulnerable › Vulnerabilities

CVE-2026-41238: DOMPurify: Prototype Pollution to XSS Bypass via CUSTOM_ELEMENT_HANDLING Fallback

• Severity: medium (CVSS 6.9 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.2% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-04-23 · updated 2026-10-26
• Weakness: CWE-79

Description

DOMPurify 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.

Affected products

• cure53 DOMPurify: from 3.0.1, < 3.4.0

References

• https://github.com/cure53/DOMPurify/releases/tag/3.4.0
• https://github.com/cure53/DOMPurify/security/advisories/GHSA-v9jr-rg53-9pgp
• https://github.com/cure53/DOMPurify/security/advisories/GHSA-v9jr-rg53-9pgp

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