Package Instance

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).

DOMPurify USE_PROFILES prototype pollution allows event handlers
## Summary
When `USE_PROFILES` is enabled, DOMPurify rebuilds `ALLOWED_ATTR` as a plain array before populating it with the requested allowlists. Because the sanitizer still looks up attributes via `ALLOWED_ATTR[lcName]`, any `Array.prototype` property that is polluted also counts as an allowlisted attribute. An attacker who can set `Array.prototype.onclick = true` (or a runtime already subject to prototype pollution) can thus force DOMPurify to keep event handlers such as `onclick` even when they are normally forbidden. The provided PoC sanitizes `<img onclick=...>` with `USE_PROFILES` and adds the sanitized output to the DOM; the polluted prototype allows the event handler to survive and execute, turning what should be a blocklist into a silent XSS vector.

## Impact
Prototype pollution makes DOMPurify accept dangerous event handler attributes, which bypasses the sanitizer and results in DOM-based XSS once the sanitized markup is rendered.

## Credits
Identified by Cantina’s Apex (https://www.cantina.security).

DOMPurify contains a Cross-site Scripting vulnerability
DOMPurify 3.1.3 through 3.3.1 and 2.5.3 through 2.5.8, fixed in 2.5.9 and 3.3.2, contain a cross-site scripting vulnerability that allows attackers to bypass attribute sanitization by exploiting five missing rawtext elements (noscript, xmp, noembed, noframes, iframe) in the `SAFE_FOR_XML` regex. Attackers can include payloads like `</noscript><img src=x onerror=alert(1)>` in attribute values to execute JavaScript when sanitized output is placed inside these unprotected rawtext contexts.