Extra DOM Clobbering protection via SANITIZE_NAMED_PROPS config

README.md

@@ -43,7 +43,7 @@ let clean = DOMPurify.sanitize(dirty);
 Or maybe this, if you love working with Angular or alike:
 
 ```js
-import * as DOMPurify from 'dompurify'
+import * as DOMPurify from 'dompurify';
 
 let clean = DOMPurify.sanitize('<b>hello there</b>');
 ```
@@ -298,6 +298,11 @@ var clean = DOMPurify.sanitize(dirty, {WHOLE_DOCUMENT: true});
 // disable DOM Clobbering protection on output (default is true, handle with care, minor XSS risks here)
 var clean = DOMPurify.sanitize(dirty, {SANITIZE_DOM: false});
 
+// enforce strict DOM Clobbering protection via namespace isolation (default is false)
+// when enabled, isolates the namespace of named properties (i.e., `id` and `name` attributes) 
+// from JS variables by prefixing them with the string `user-content-` 
+var clean = DOMPurify.sanitize(dirty, {SANITIZE_NAMED_PROPS: true});
+
 // keep an element's content when the element is removed (default is true)
 var clean = DOMPurify.sanitize(dirty, {KEEP_CONTENT: false});
 

src/purify.js

@@ -266,9 +266,27 @@ function createDOMPurify(window = getGlobal()) {
    * case Trusted Types are not supported  */
   let RETURN_TRUSTED_TYPE = false;
 
-  /* Output should be free from DOM clobbering attacks? */
+  /* Output should be free from DOM clobbering attacks?
+   * This sanitizes markups named with colliding, clobberable built-in DOM APIs.
+   */
   let SANITIZE_DOM = true;
 
+  /* Achieve full DOM Clobbering protection by isolating the namespace of named
+   * properties and JS variables, mitigating attacks that abuse the HTML/DOM spec rules.
+   *
+   * HTML/DOM spec rules that enable DOM Clobbering:
+   *   - Named Access on Window (§7.3.3)
+   *   - DOM Tree Accessors (§3.1.5)
+   *   - Form Element Parent-Child Relations (§4.10.3)
+   *   - Iframe srcdoc / Nested WindowProxies (§4.8.5)
+   *   - HTMLCollection (§4.2.10.2)
+   *
+   * Namespace isolation is implemented by prefixing `id` and `name` attributes
+   * with a constant string, i.e., `user-content-`
+   */
+  let SANITIZE_NAMED_PROPS = false;
+  const SANITIZE_NAMED_PROPS_PREFIX = 'user-content-';
+
   /* Keep element content when removing element? */
   let KEEP_CONTENT = true;
 
@@ -443,6 +461,7 @@ function createDOMPurify(window = getGlobal()) {
     RETURN_TRUSTED_TYPE = cfg.RETURN_TRUSTED_TYPE || false; // Default false
     FORCE_BODY = cfg.FORCE_BODY || false; // Default false
     SANITIZE_DOM = cfg.SANITIZE_DOM !== false; // Default true
+    SANITIZE_NAMED_PROPS = cfg.SANITIZE_NAMED_PROPS || false; // Default false
     KEEP_CONTENT = cfg.KEEP_CONTENT !== false; // Default true
     IN_PLACE = cfg.IN_PLACE || false; // Default false
     IS_ALLOWED_URI = cfg.ALLOWED_URI_REGEXP || IS_ALLOWED_URI;
@@ -1205,6 +1224,17 @@ function createDOMPurify(window = getGlobal()) {
         continue;
       }
 
+      /* Full DOM Clobbering protection via namespace isolation,
+       * Prefix id and name attributes with `user-content-`
+       */
+      if (SANITIZE_NAMED_PROPS && (lcName === 'id' || lcName === 'name')) {
+        // Remove the attribute with this value
+        _removeAttribute(name, currentNode);
+
+        // Prefix the value and later re-create the attribute with the sanitized value
+        value = SANITIZE_NAMED_PROPS_PREFIX + value;
+      }
+
       /* Handle attributes that require Trusted Types */
       if (
         trustedTypesPolicy &&

test/test-suite.js

@@ -465,6 +465,27 @@
         ['', '<form><input name="attributes"></form>', '<form><input></form>']
       );
     });
+    QUnit.test('Config-Flag tests: SANITIZE_NAMED_PROPS', function (assert) {
+      // SANITIZE_NAMED_PROPS
+      assert.equal(
+        DOMPurify.sanitize('<a id="x"></a>', {
+          SANITIZE_NAMED_PROPS: true,
+        }),
+        '<a id="user-content-x"></a>'
+      );
+      assert.equal(
+        DOMPurify.sanitize('<form id="x"><input id="y"></form>', {
+          SANITIZE_NAMED_PROPS: true,
+        }),
+        '<form id="user-content-x"><input id="user-content-y"></form>'
+      );
+      assert.equal(
+        DOMPurify.sanitize('<a id="x"></a><a id="x"></a>', {
+          SANITIZE_NAMED_PROPS: true,
+        }),
+        '<a id="user-content-x"></a><a id="user-content-x"></a>'
+      );
+    });
     QUnit.test('Config-Flag tests: WHOLE_DOCUMENT', function (assert) {
       //WHOLE_DOCUMENT
       assert.equal(DOMPurify.sanitize('123', { WHOLE_DOCUMENT: false }), '123');