Severity
Details
- CVSS score
- 5.1
- CVSS vector
- CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Overview
About vulnerability
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).