fixup! fix(@angular/ssr): validate host headers to prevent header-based SSRF

Author: alan-agius4

packages/angular/ssr/BUILD.bazel

@@ -20,7 +20,7 @@ ts_project(
     ),
     args = [
         "--lib",
-        "dom,es2022",
+        "dom.iterable,dom,es2022",
     ],
     data = [
         "//packages/angular/ssr/third_party/beasties:beasties_bundled",

packages/angular/ssr/node/src/common-engine/common-engine.ts

@@ -99,7 +99,7 @@ export class CommonEngine {
             'Please provide a list of allowed hosts in the "allowedHosts" option in the "CommonEngine" constructor.',
           isAllowedHostConfigured
             ? ''
-            : '\nFallbacking to client side rendering. This will become a 400 Bad Request in a future major version.',
+            : '\nFalling back to client side rendering. This will become a 400 Bad Request in a future major version.',
         );
 
         if (!isAllowedHostConfigured) {

packages/angular/ssr/src/app-engine.ts

@@ -270,7 +270,7 @@ export class AngularAppEngine {
         errorMessage +
         (isAllowedHostConfigured
           ? ''
-          : '\nFallbacking to client side rendering. This will become a 400 Bad Request in a future major version.') +
+          : '\nFalling back to client side rendering. This will become a 400 Bad Request in a future major version.') +
         '\n\nFor more information, see https://angular.dev/best-practices/security#preventing-server-side-request-forgery-ssrf',
     );
 

packages/angular/ssr/src/utils/validation.ts

@@ -93,32 +93,88 @@ export function cloneRequestAndPatchHeaders(
   });
 
   const headers = clonedReq.headers;
-  const originalHeadersGet = headers.get;
 
+  const originalGet = headers.get;
   // eslint-disable-next-line @typescript-eslint/no-unnecessary-type-assertion
-  (headers.get as typeof originalHeadersGet) = (name: string): string | null => {
-    const value = originalHeadersGet.call(headers, name);
+  (headers.get as typeof originalGet) = function (name) {
+    const value = originalGet.call(headers, name);
     if (!value) {
       return value;
     }
 
-    const key = name.toLowerCase();
-    if (HOST_HEADERS_TO_VALIDATE.has(key)) {
-      try {
-        verifyHostAllowed(key, value, allowedHosts);
-      } catch (error) {
-        onError(error as Error);
+    validateHeader(name, value, allowedHosts, onError);
 
-        return null;
-      }
+    return value;
+  };
+
+  const originalValues = headers.values;
+  // eslint-disable-next-line @typescript-eslint/no-unnecessary-type-assertion
+  (headers.values as typeof originalValues) = function () {
+    for (const name of HOST_HEADERS_TO_VALIDATE) {
+      validateHeader(name, originalGet.call(headers, name), allowedHosts, onError);
     }
 
-    return value;
+    return originalValues.call(headers);
+  };
+
+  const originalEntries = headers.entries;
+  // eslint-disable-next-line @typescript-eslint/no-unnecessary-type-assertion
+  (headers.entries as typeof originalEntries) = function () {
+    const iterator = originalEntries.call(headers);
+
+    return {
+      next() {
+        const result = iterator.next();
+        if (!result.done) {
+          const [key, value] = result.value;
+          validateHeader(key, value, allowedHosts, onError);
+        }
+
+        return result;
+      },
+      [Symbol.iterator]() {
+        return this;
+      },
+    };
   };
 
+  // Ensure for...of loops use the new patched entries
+  (headers[Symbol.iterator] as typeof originalEntries) = headers.entries;
+
   return { request: clonedReq, onError: onErrorPromise };
 }
 
+/**
+ * Validates a specific header value against the allowed hosts.
+ * @param name - The name of the header to validate.
+ * @param value - The value of the header to validate.
+ * @param allowedHosts - A set of allowed hostnames.
+ * @param onError - A callback function to call if the header value is invalid.
+ * @throws Error if the header value is invalid.
+ */
+function validateHeader(
+  name: string,
+  value: string | null,
+  allowedHosts: ReadonlySet<string>,
+  onError: (value: Error) => void,
+): void {
+  if (!value) {
+    return;
+  }
+
+  if (!HOST_HEADERS_TO_VALIDATE.has(name.toLowerCase())) {
+    return;
+  }
+
+  try {
+    verifyHostAllowed(name, value, allowedHosts);
+  } catch (error) {
+    onError(error as Error);
+
+    throw error;
+  }
+}
+
 /**
  * Validates a specific host header value against the allowed hosts.
  *

packages/angular/ssr/test/utils/validation_spec.ts

@@ -135,7 +135,9 @@ describe('Validation Utils', () => {
       });
       const { request: secured, onError } = cloneRequestAndPatchHeaders(req, allowedHosts);
 
-      expect(secured.headers.get('host')).toBeNull();
+      expect(() => secured.headers.get('host')).toThrowError(
+        'Header "host" with value "evil.com" is not allowed.',
+      );
       await expectAsync(onError).toBeResolvedTo(
         jasmine.objectContaining({
           message: jasmine.stringMatching('Header "host" with value "evil.com" is not allowed'),
@@ -157,7 +159,9 @@ describe('Validation Utils', () => {
       });
       const { request: secured, onError } = cloneRequestAndPatchHeaders(req, allowedHosts);
 
-      expect(secured.headers.get('x-forwarded-host')).toBeNull();
+      expect(() => secured.headers.get('x-forwarded-host')).toThrowError(
+        'Header "x-forwarded-host" with value "evil.com" is not allowed.',
+      );
       await expectAsync(onError).toBeResolvedTo(
         jasmine.objectContaining({
           message: jasmine.stringMatching(
@@ -175,5 +179,62 @@ describe('Validation Utils', () => {
 
       expect(secured.headers.get('accept')).toBe('application/json');
     });
+
+    it('should validate headers when iterating with entries()', async () => {
+      const req = new Request('http://example.com', {
+        headers: { 'host': 'evil.com' },
+      });
+      const { request: secured, onError } = cloneRequestAndPatchHeaders(req, allowedHosts);
+
+      expect(() => {
+        for (const _ of secured.headers.entries()) {
+          // access the header to trigger the validation
+        }
+      }).toThrowError('Header "host" with value "evil.com" is not allowed.');
+
+      await expectAsync(onError).toBeResolvedTo(
+        jasmine.objectContaining({
+          message: jasmine.stringMatching('Header "host" with value "evil.com" is not allowed.'),
+        }),
+      );
+    });
+
+    it('should validate headers when iterating with values()', async () => {
+      const req = new Request('http://example.com', {
+        headers: { 'host': 'evil.com' },
+      });
+      const { request: secured, onError } = cloneRequestAndPatchHeaders(req, allowedHosts);
+
+      expect(() => {
+        for (const _ of secured.headers.values()) {
+          // access the header to trigger the validation
+        }
+      }).toThrowError('Header "host" with value "evil.com" is not allowed.');
+
+      await expectAsync(onError).toBeResolvedTo(
+        jasmine.objectContaining({
+          message: jasmine.stringMatching('Header "host" with value "evil.com" is not allowed.'),
+        }),
+      );
+    });
+
+    it('should validate headers when iterating with for...of', async () => {
+      const req = new Request('http://example.com', {
+        headers: { 'host': 'evil.com' },
+      });
+      const { request: secured, onError } = cloneRequestAndPatchHeaders(req, allowedHosts);
+
+      expect(() => {
+        for (const _ of secured.headers) {
+          // access the header to trigger the validation
+        }
+      }).toThrowError('Header "host" with value "evil.com" is not allowed.');
+
+      await expectAsync(onError).toBeResolvedTo(
+        jasmine.objectContaining({
+          message: jasmine.stringMatching('Header "host" with value "evil.com" is not allowed.'),
+        }),
+      );
+    });
   });
 });