DOMPurify SAFE_FOR_TEMPLATES bypass: split template expressions survive in attached shadow root content on DOM output modes
## Summary
When DOMPurify is configured with `SAFE_FOR_TEMPLATES: true` together with a DOM-returning mode (`RETURN_DOM: true`, `RETURN_DOM_FRAGMENT: true`, or `IN_PLACE: true`), template expressions such as `{{...}}`, `${...}`, and `<%...%>` survive sanitization inside the text content of an attached shadow root. The post-walk safety net `_scrubTemplateExpressions` (`src/purify.ts:1717`) was extended to recurse into `<template>.content`, but it never recurses into attached shadow roots. An attacker who can supply a DOM node carrying a shadow root (the `IN_PLACE` and shadow-aware `RETURN_DOM` surfaces) can split an expression across text nod
DOMPurify IN_PLACE: hook that removes a parent or sibling leaves the detached subtree's event handlers armed (incomplete fix for GHSA-p98j-92pf-mc4p)
### Summary
The 3.4.16 fix for GHSA-p98j-92pf-mc4p only covers a hook that removes the node it was called for. If an `IN_PLACE` hook removes a different node, like the current node's parent or a sibling that has not been visited yet, that subtree is never walked or neutralized. Event handlers in it stay on the elements, and an `<img onerror>` that was already loading fires after `sanitize()` returns.
The README says: "Nodes that a hook detaches from the tree ... are treated as removed. In IN_PLACE mode their subtree is neutralized inline, so an `<img onload>` that was already loading when you built the live tree cannot fire after `sanitize(
DOMPurify: SMIL attributeName=href guard is skipped when PARSER_MEDIA_TYPE is application/xhtml+xml
### Summary
DOMPurify drops `attributeName` attributes whose value contains `href`, so an allowed `<animate>` or `<set>` can't rewrite a link's href after sanitizing. The check compares the attribute name after `transformCaseFunc`, and that function doesn't lowercase in XHTML mode. In XHTML the attribute is spelled `attributeName`, so the comparison with `"attributename"` never matches and the guard does nothing.
An app that uses `PARSER_MEDIA_TYPE: 'application/xhtml+xml'` and allows `animate` and `attributeName` will keep `<animate attributeName="href" values="x;javascript:alert(1)">`. Clicking the parent link then runs the script.
This
DOMPurify before 3.4.16 XSS via IN_PLACE Returned Rawtext Root
DOMPurify before 3.4.16 contains a cross-site scripting vulnerability that allows attackers to bypass sanitization because IN_PLACE mode returns a force-removed style element whose text content still carries markup. Attackers can supply a style element containing a closing style tag and an img onerror payload, which executes script when the application serializes and re-parses the returned node.
DOMPurify before 3.4.13 Cross-Site Scripting via IN_PLACE hook
DOMPurify before 3.4.13 contains a cross-site scripting vulnerability in IN_PLACE sanitization where element-removal hooks fail to neutralize detached subtrees. Attackers can supply HTML with event handlers on descendant elements that execute after sanitization completes, even though the returned root appears clean.
DOMPurify before 3.4.12 Hook Bypass via CUSTOM_ELEMENT_HANDLING
DOMPurify before 3.4.12 fails to execute afterSanitizeElements hook for custom elements allowed via CUSTOM_ELEMENT_HANDLING.tagNameCheck, allowing attributes to bypass application security policies. Attackers can preserve sensitive attributes on custom elements that later re-inject them into innerHTML sinks, creating second-order XSS gadgets.
DOMPurify before 3.4.8 Template Expression Injection via RETURN_DOM
DOMPurify versions >=3.0.0 and before 3.4.8, when configured with SAFE_FOR_TEMPLATES together with a DOM output mode (RETURN_DOM, RETURN_DOM_FRAGMENT, or IN_PLACE), fail to strip template expressions (e.g. ${evil}, {{evil}}, <%evil%>) inside <template> element content. The final normalization/scrub pass (_scrubTemplateExpressions) uses a NodeIterator and node.normalize() that do not descend into template.content, so expressions that only form after adjacent text nodes merge survive sanitization. This bypasses SAFE_FOR_TEMPLATES and can allow a downstream template engine to evaluate attacker-supplied expressions. The string output path is not
DOMPurify before 3.4.9 Trusted Types Policy State Contamination
DOMPurify 3.0.0 before 3.4.9 does not reset the retained Trusted Types policy when clearConfig() is called, so a DOMPurify instance reused across trust boundaries stays bound to a previously supplied TRUSTED_TYPES_POLICY. A later caller that requests RETURN_TRUSTED_TYPE output receives a TrustedHTML object created by the old (potentially unsafe) policy rather than a clean default, which can lead to script execution at a Trusted Types sink. Passing TRUSTED_TYPES_POLICY: null on the later call also does not clear the retained policy.
DOMPurify before 3.4.11 Permanent Attribute Allowlist Pollution via setConfig
DOMPurify before 3.4.11 fails to clone the ALLOWED_ATTR allowlist when setConfig() is used with an uponSanitizeAttribute hook, allowing the hook to permanently mutate the shared allowlist. Attackers can register a hook that conditionally allows dangerous attributes like onerror for trusted elements, then submit untrusted content that inherits the polluted allowlist and executes event handlers as stored XSS.