DOMPurify before 3.3.2 contains a URI validation bypass vulnerability when ADD_ATTR is provided as a predicate function via EXTRA_ELEMENT_HANDLING.attributeCheck. Attackers can supply a predicate that accepts specific attribute and tag combinations to bypass URI-safe validation, allowing unsafe protocols like javascript: to survive sanitization and execute as DOM-based XSS when the link is activated.

Affected: npm: dompurify

## 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).

fast-uri: Fast-uri: Security policy bypass due to URL parsing inconsistency baseline-browser-mapping: baseline-browser-mapping: Denial of Service via improper input handling DOMPurify: DOMPurify: Cross-Site Scripting via unsanitized DOM elements from different realms DOMPurify: DOMPurify: Cross-site scripting due to state leakage in sanitization. dompurify: DOMPurify: URI validation bypass leads to cross-site scripting dompurify: DOMPurify: Cross-Site Scripting (XSS) via prototype pollution in USE_PROFILES mode dompurify: DOMPurify: Cross-Site Scripting vulnerability allows arbitrary code execution browserslist: Browserslist: Prototype pollution leading to denial of service browserslist: Browserslist: Denial of Service via unbounded memory growth from distinct query results

Affected: Ubuntu:22.04:LTS: node-dompurify, Ubuntu:24.04:LTS: node-dompurify

DOMPurify before 3.3.2 contains a URI validation bypass vulnerability when ADD_ATTR is provided as a predicate function via EXTRA_ELEMENT_HANDLING.attributeCheck. Attackers can supply a predicate that accepts specific attribute and tag combinations to bypass URI-safe validation, allowing unsafe protocols like javascript: to survive sanitization and execute as DOM-based XSS when the link is activated.