Update dependency dompurify to >=3.4.13 [SECURITY]

[renovate-bot-justlab]

This PR contains the following updates:

Package	Change	Age	Confidence
dompurify	>=3.4.11 → >=3.4.13

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DOMPurify: CUSTOM_ELEMENT_HANDLING bypasses afterSanitizeElements for allowed custom elements.

GHSA-c2j3-45gr-mqc4

More information

Details

Summary

There is a possible hook-policy inconsistency in DOMPurify 3.4.11 involving CUSTOM_ELEMENT_HANDLING.

When a custom element is allowed via CUSTOM_ELEMENT_HANDLING.tagNameCheck, it appears that the element does not go through afterSanitizeElements in the same way as a normal element. As a result, an application that relies on afterSanitizeElements as a security policy layer to strip sensitive attributes from all elements may see those attributes removed from normal elements but preserved on allowed custom elements.

This does not appear to be a direct DOMPurify XSS or a case where DOMPurify directly allows executable payloads. The preserved value is still inert at sanitize time. The issue becomes relevant when the allowed custom element later re-injects that attribute value into an HTML sink such as innerHTML, creating a second-order XSS gadget.

Details

The issue appears to originate from the control flow in src/purify.ts: line 1672~1691

const _sanitizeDisallowedNode = function (
    currentNode: any,
    tagName: string
  ): boolean {
    /* Check if we have a custom element to handle */
    if (!FORBID_TAGS[tagName] && _isBasicCustomElement(tagName)) {
      if (
        CUSTOM_ELEMENT_HANDLING.tagNameCheck instanceof RegExp &&
        regExpTest(CUSTOM_ELEMENT_HANDLING.tagNameCheck, tagName)
      ) {
        return false;
      }

      if (
        CUSTOM_ELEMENT_HANDLING.tagNameCheck instanceof Function &&
        CUSTOM_ELEMENT_HANDLING.tagNameCheck(tagName)
      ) {
        return false;
      }
    }

CUSTOM_ELEMENT_HANDLING is parsed from user configuration at src/purify.ts: line 741~748

const customElementHandling =
      objectHasOwnProperty(cfg, 'CUSTOM_ELEMENT_HANDLING') &&
      cfg.CUSTOM_ELEMENT_HANDLING &&
      typeof cfg.CUSTOM_ELEMENT_HANDLING === 'object'
        ? clone(cfg.CUSTOM_ELEMENT_HANDLING)
        : create(null);

    CUSTOM_ELEMENT_HANDLING = create(null);

In particular, tagNameCheck, attributeNameCheck, and allowCustomizedBuiltInElements are copied into the internal CUSTOM_ELEMENT_HANDLING object there.

During element sanitization, _sanitizeElements() checks whether a node is forbidden or not allowlisted at src/purify.ts: line 1805~1814

/* Remove element if anything forbids its presence */
    if (
      FORBID_TAGS[tagName] ||
      (!(
        EXTRA_ELEMENT_HANDLING.tagCheck instanceof Function &&
        EXTRA_ELEMENT_HANDLING.tagCheck(tagName)
      ) &&
        !ALLOWED_TAGS[tagName])
    ) {
      return _sanitizeDisallowedNode(currentNode, tagName);
    }

If so, it immediately delegates to _sanitizeDisallowedNode(currentNode, tagName) and returns its boolean result.

Inside _sanitizeDisallowedNode(), the custom-element-specific allow path is implemented at src/purify.ts: line 1672~1692

const _sanitizeDisallowedNode = function (
    currentNode: any,
    tagName: string
  ): boolean {
    /* Check if we have a custom element to handle */
    if (!FORBID_TAGS[tagName] && _isBasicCustomElement(tagName)) {
      if (
        CUSTOM_ELEMENT_HANDLING.tagNameCheck instanceof RegExp &&
        regExpTest(CUSTOM_ELEMENT_HANDLING.tagNameCheck, tagName)
      ) {
        return false;
      }

      if (
        CUSTOM_ELEMENT_HANDLING.tagNameCheck instanceof Function &&
        CUSTOM_ELEMENT_HANDLING.tagNameCheck(tagName)
      ) {
        return false;
      }
    }

If the node is treated as a basic custom element and CUSTOM_ELEMENT_HANDLING.tagNameCheck matches, the function returns false immediately at line 1682 or 1689, meaning “do not remove this node”.

That early return false is significant because control returns directly to _sanitizeElements() via the return _sanitizeDisallowedNode(...) at line 1813. As a result, the later logic in _sanitizeElements() is skipped for that custom element instance, including:

• the namespace validation at src/purify.ts: line 1816~1826

* Check whether element has a valid namespace.
       Realm-safe check (GHSA-hpcv-96wg-7vj8): use the cached Node.prototype
       nodeType getter rather than `instanceof Element`, which is realm-
       bound and short-circuits to false for any node minted in a different
       realm — letting a foreign-realm element with a forbidden namespace
       slip past the namespace check entirely. */
    const nt = getNodeType ? getNodeType(currentNode) : currentNode.nodeType;
    if (nt === NODE_TYPE.element && !_checkValidNamespace(currentNode)) {
      _forceRemove(currentNode);
      return true;
    }

• the fallback-tag mXSS check at src/purify.ts: line 1828~1837

/* Make sure that older browsers don't get fallback-tag mXSS */
    if (
      (tagName === 'noscript' ||
        tagName === 'noembed' ||
        tagName === 'noframes') &&
      regExpTest(EXPRESSIONS.FALLBACK_TAG_CLOSE, currentNode.innerHTML)
    ) {
      _forceRemove(currentNode);
      return true;
    }

• most importantly for this report, the afterSanitizeElements hook dispatch at src/purify.ts: line 1850~1851.

   /* Execute a hook if present */
    _executeHooks(hooks.afterSanitizeElements, currentNode, null);

In other words, a normal allowlisted element continues through _sanitizeElements() and reaches hooks.afterSanitizeElements, but a disallowed-by-default element that is revived by the CUSTOM_ELEMENT_HANDLING.tagNameCheck path does not. This creates a policy inconsistency: an application that relies on afterSanitizeElements to remove an attribute from all elements will observe that the policy is applied to normal elements but not to custom elements allowed through CUSTOM_ELEMENT_HANDLING.

In the PoC, the application hook removes data-bio from ordinary elements, but the same attribute remains on <x-bio> because the custom-element keep path bypasses afterSanitizeElements. The attribute itself is inert at sanitize time and DOMPurify is not directly allowing executable SVG/HTML through. The security impact appears when the application-defined custom element later reads the preserved data-bio value in connectedCallback() and writes it to innerHTML, turning the preserved attribute into a second-order XSS gadget.

PoC

Reproduced on DOMPurify 3.4.11.

Steps

1. Save the following HTML to a file, for example poc.html.
2. Open it in a browser.
3. Observe that the div control loses data-bio, while the allowed custom element keeps it.
4. Observe that after connectedCallback() runs, the candidate payload is reinserted into the DOM and executes through the custom element’s own sink.

HTML PoC

<!DOCTYPE html>
<html>
<head>
  <meta charset="UTF-8">
  <script src="https://cdnjs.cloudflare.com/ajax/libs/dompurify/3.4.11/purify.min.js"></script>
</head>
<body>
<pre id="result"></pre>

<script>
window.__controlFired = false;
window.__candidateFired = false;

customElements.define("x-bio", class extends HTMLElement {
  connectedCallback() {
    const bio = this.getAttribute("data-bio");
    if (bio) this.innerHTML = bio;
  }
});

DOMPurify.addHook("afterSanitizeElements", node => {
  if (node.hasAttribute && node.hasAttribute("data-bio")) {
    node.removeAttribute("data-bio");
  }
});

const config = {
  CUSTOM_ELEMENT_HANDLING: {
    tagNameCheck: /^x-/
  }
};

const controlInput =
  '<div data-bio="&lt;img src=x onerror=window.__controlFired=true&gt;"></div>';

const candidateInput =
  '<x-bio data-bio="&lt;img src=x onerror=window.__candidateFired=true&gt;"></x-bio>';

const cleanControl = DOMPurify.sanitize(controlInput, config);
const cleanCandidate = DOMPurify.sanitize(candidateInput, config);

const container = document.createElement("div");
container.innerHTML = cleanCandidate;
document.body.appendChild(container);

setTimeout(() => {
  document.getElementById("result").textContent =
    "This is not direct DOMPurify XSS.\n" +
    "The payload becomes executable only after x-bio writes data-bio into innerHTML.\n\n" +
    "control: " + cleanControl + "\n" +
    "candidate: " + cleanCandidate + "\n" +
    "after connectedCallback: " + container.innerHTML + "\n" +
    "control fired: " + window.__controlFired + "\n" +
    "candidate fired: " + window.__candidateFired;
}, 100);
</script>
</body>
</html>

Expected result

control: <div></div>
candidate: <x-bio data-bio="<img src=x onerror=window.__candidateFired=true>"></x-bio>
after connectedCallback: <x-bio data-bio="..."><img src="x" onerror="window.__candidateFired=true"></x-bio>
control fired: false
candidate fired: true

This is output of HTML PoC.

Impact

This does not appear to affect DOMPurify’s default configuration as a direct sanitizer bypass.

The impact is limited to applications that:

• enable CUSTOM_ELEMENT_HANDLING,
• rely on afterSanitizeElements as a security policy layer,
• expect that hook to apply uniformly to all surviving elements,
• and have allowed custom elements that later re-inject preserved attribute values into innerHTML or another HTML sink.

In that situation, the behavior can become a second-order XSS gadget because a security-relevant attribute is removed from normal elements but remains on allowed custom elements.

Possible fixes or mitigations might include

• ensuring that allowed custom elements also consistently pass through afterSanitizeElements
• documenting clearly that elements preserved via CUSTOM_ELEMENT_HANDLING may not participate in the same post-element hook flow as normal allowlisted elements.

Severity

• CVSS Score: 2.1 / 10 (Low)
• Vector String: CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:A/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N

References

• https://github.com/cure53/DOMPurify/security/advisories/GHSA-c2j3-45gr-mqc4
• https://github.com/cure53/DOMPurify/pull/1537
• https://github.com/cure53/DOMPurify/commit/a9ca1e537422319a557a9a2aa61f003b23b4a197
• https://github.com/cure53/DOMPurify/releases/tag/3.4.12
• https://github.com/advisories/GHSA-c2j3-45gr-mqc4

This data is provided by the GitHub Advisory Database (CC-BY 4.0).

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DOMPurify: IN_PLACE hook removal leaves a detached subtree executable, causing XSS

GHSA-55q2-fjhq-7xh7

More information

Details

Summary

During IN_PLACE sanitization, a hook that removes an element can leave that element's detached descendants executable. A descendant image can retain its attacker-provided onload handler and fire after sanitize() returns, even though the returned root is clean and the image remains disconnected from the document.

Details

In DOMPurify 3.4.12, _sanitizeElements() in src/purify.ts:1862-1904 runs the beforeSanitizeElements or uponSanitizeElement hook and returns immediately when the hook detached the current node. The return does not call _neutralizeSubtree(currentNode).

The detached subtree is not added to DOMPurify.removed, so the post-walk IN_PLACE neutralization cannot reach it. If the browser queued a resource event while the application constructed the detached dirty root, a descendant can therefore retain its handler and execute after sanitization.

The hook only rejects the containing element and does not add or approve the event handler. DOMPurify's ordinary removal path de-arms the same queued event; only the hook-detachment early return skips the existing subtree neutralization.

PoC

Load the published dompurify@3.4.12 dist/purify.js before this script in Chromium:

<div id="result">not fired</div>
<script>
const root = document.createElement('div');
root.innerHTML = `
  <footer>
    <img src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7"
         onload="result.textContent = 'XSS after sanitize'">
  </footer>
  <div>safe</div>`;

DOMPurify.setConfig({
  ALLOWED_TAGS: ['div', '#text', 'footer'],
  IN_PLACE: true
});
DOMPurify.addHook('uponSanitizeElement', node => {
  if (node.tagName === 'FOOTER') node.remove();
});

DOMPurify.sanitize(root);
document.body.append(root);
</script>

sanitize() returns with no handler execution and the returned root contains only the safe div. After the event loop advances, the original image remains disconnected but its retained onload changes the page to XSS after sanitize.

As the claim-matched control, use the same detached input with ALLOWED_TAGS: ['div', '#text'] and no hook. DOMPurify's ordinary removal path removes the original image's handler, the returned root is still <div>safe</div>, and the marker does not fire.

Impact

In an application that uses IN_PLACE with the documented element-removal hook pattern, an attacker who can supply HTML can execute JavaScript in the integrating application's origin after the application sanitizes and renders that content.

The required non-default configuration is IN_PLACE plus a hook that removes a containing element. The hook does not add or approve the event handler, and the dirty root never needs to be connected before sanitization.

Suggested fix

Reuse the existing _neutralizeSubtree(currentNode) helper before returning from both hook-detachment branches in _sanitizeElements(). Add regressions for beforeSanitizeElements and uponSanitizeElement that retain a reference to a descendant resource element and verify that its event handler is removed after the hook detaches its ancestor.

Severity

• CVSS Score: 5.1 / 10 (Medium)
• Vector String: CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:P/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N

References

• https://github.com/cure53/DOMPurify/security/advisories/GHSA-55q2-fjhq-7xh7
• https://github.com/cure53/DOMPurify/pull/1557
• https://github.com/cure53/DOMPurify/commit/3067f7746769
• https://github.com/cure53/DOMPurify/releases/tag/3.4.13
• https://github.com/advisories/GHSA-55q2-fjhq-7xh7

This data is provided by the GitHub Advisory Database (CC-BY 4.0).

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Release Notes

cure53/DOMPurify (dompurify)

v3.4.13: DOMPurify 3.4.13

Compare Source

• Fixed an issue with hook removal during IN_PLACE sanitization, thanks @​koyokr
• Fixed an issue with hooks potentially bypassing the clone guard, thanks @​AkshayjainG
• Fixed an issue with DOM clobbering via ownerDocument during IN_PLACE, thanks @​AkshayjainG
• Bumped several dependencies where possible

v3.4.12: DOMPurify 3.4.12

Compare Source

• Fixed an issue where a hook would not get called for custom elements, thanks @​Rikuxx0
• Hardened the handling of hooks removing elements, @​mkrause-bee360
• Added support for a few new SVG attributes, thanks @​cbn-falias & @​Develop-KIM
• Hardened the handling of declarative partial updates
• Updated the documentation is several spots, README, wiki, etc.
• Bumped several dependencies where possible

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