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

April 22, 2026 (updated April 27, 2026)

DOMPurify versions 3.0.1 through 3.3.3 (latest) 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.

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Code Behaviors & Features

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