new and interesting iframe validation exploits

apostrophecms · Jan 26, 2021 · 54851d0 · 54851d0
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diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -1,7 +1,10 @@
 # Changelog
 
+## 2.3.2 (2021-01-26):
+- Additional fixes for iframe validation exploits. Prevent exploits based on browsers' tolerance of the use of "\" rather than "/" and the presence of whitespace at this point in the URL. Thanks to Ron Masas of <a href="https://www.checkmarx.com/">Checkmarx</a> for pointing out the issue and writing unit tests.
+
 ## 2.3.1 (2021-01-22):
-- Uses the standard WHATWG URL parser to stop IDNA (Internationalized Domain Name) attacks on the iframe hostname validator. Thanks to Ron Masas of Checkmarx for pointing out the issue and suggesting the use of the WHATWG parser.
+- Uses the standard WHATWG URL parser to stop IDNA (Internationalized Domain Name) attacks on the iframe hostname validator. Thanks to Ron Masas of <a href="https://www.checkmarx.com/">Checkmarx</a> for pointing out the issue and suggesting the use of the WHATWG parser.
 
 ## 2.3.0 (2020-12-16):
 - Upgrades `htmlparser2` to new major version `^6.0.0`. Thanks to [Bogdan Chadkin](https://github.com/TrySound) for the contribution.

diff --git a/index.js b/index.js
@@ -304,6 +304,10 @@ function sanitizeHtml(html, options, _recursing) {
             if (name === 'iframe' && a === 'src') {
               let allowed = true;
               try {
+                // Chrome accepts \ as a substitute for / in the // at the
+                // start of a URL, so rewrite accordingly to prevent exploit.
+                // Also drop any whitespace at that point in the URL
+                value = value.replace(/^(\w+:)?\s*[\\/]\s*[\\/]/, '$1//');
                 if (value.startsWith('relative:')) {
                   // An attempt to exploit our workaround for base URLs being
                   // mandatory for relative URL validation in the WHATWG

diff --git a/package.json b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "sanitize-html",
-  "version": "2.3.1",
+  "version": "2.3.2",
   "description": "Clean up user-submitted HTML, preserving whitelisted elements and whitelisted attributes on a per-element basis",
   "sideEffects": false,
   "main": "index.js",

diff --git a/test/test.js b/test/test.js
@@ -1269,4 +1269,60 @@ describe('sanitizeHtml', function() {
       '<iframe></iframe>'
     );
   });
+  it('Should prevent hostname bypass using protocol-relative src', function () {
+    assert.strictEqual(
+      sanitizeHtml('<iframe src="/\\example.com"></iframe>', {
+        allowedTags: ['iframe'],
+        allowedAttributes: {
+          iframe: ['src']
+        },
+        allowedIframeHostnames: ["www.youtube.com"],
+        allowIframeRelativeUrls: true
+      }), '<iframe></iframe>'
+    );
+    assert.strictEqual(
+      sanitizeHtml('<iframe src="\\/example.com"></iframe>', {
+        allowedTags: ['iframe'],
+        allowedAttributes: {
+          iframe: ['src']
+        },
+        allowedIframeHostnames: ["www.youtube.com"],
+        allowIframeRelativeUrls: true
+      }), '<iframe></iframe>'
+    );
+    const linefeed = decodeURIComponent("%0A");
+    assert.strictEqual(
+      sanitizeHtml('<iframe src="/'+linefeed+'\\example.com"></iframe>', {
+        allowedTags: ['iframe'],
+        allowedAttributes: {
+          iframe: ['src']
+        },
+        allowedIframeHostnames: ["www.youtube.com"],
+        allowIframeRelativeUrls: true
+      }), '<iframe></iframe>'
+    );
+    const creturn = decodeURIComponent("%0D");
+    assert.strictEqual(
+      sanitizeHtml('<iframe src="/'+creturn+'\\example.com"></iframe>', {
+        allowedTags: ['iframe'],
+        allowedAttributes: {
+          iframe: ['src']
+        },
+        allowedIframeHostnames: ["www.youtube.com"],
+        allowIframeRelativeUrls: true
+      }), '<iframe></iframe>'
+    );
+    const tab = decodeURIComponent("%09");
+    assert.strictEqual(
+      sanitizeHtml('<iframe src="/'+tab+'\\example.com"></iframe>', {
+        allowedTags: ['iframe'],
+        allowedAttributes: {
+          iframe: ['src']
+        },
+        allowedIframeHostnames: ["www.youtube.com"],
+        allowIframeRelativeUrls: true
+      }), '<iframe></iframe>'
+    );
+  });
+
 });