GHSA-CJMM-F4JC-QW8R

Description

DOMPurify ADD_ATTR predicate skips URI validation ## Summary DOMPurify allows `ADD_ATTR` to be provided as a predicate function via `EXTRA_ELEMENT_HANDLING.attributeCheck`. When the predicate returns `true`, `_isValidAttribute` short-circuits the attribute check before URI-safe validation runs. An attacker who supplies a predicate that accepts specific attribute/tag combinations can then sanitize input such as `<a href="javascript:alert(document.domain)">` and have the `javascript:` URL survive, because URI validation is skipped for that attribute while other checks still pass. The provided PoC accepts `href` for anchors and then triggers a click inside an iframe, showing that the sanitized payload executes despite the protocol bypass. ## Impact Predicate-based allowlisting bypasses DOMPurify's URI validation, allowing unsafe protocols such as `javascript:` to reach the DOM and execute whenever the link is activated, resulting in DOM-based XSS. ## Credits Identified by Cantina’s Apex (https://www.cantina.security).

CVSS Metrics

• v4.0•MEDIUM•Score: 5.3CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N

Affected Systems

• Npm•dompurify

  < 3.3.2

References (3)

• https://github.com/cure53/DOMPurify/security/advisories/GHSA-cjmm-f4jc-qw8r
• https://github.com/cure53/DOMPurify
• https://github.com/cure53/DOMPurify/releases/tag/3.3.2