fix(@angular/build): escape prerender redirect URLs

Escape redirect targets before embedding them in the meta refresh tag and the fallback link of
generated static redirect pages.

Author: SkyZeroZx

packages/angular/build/src/utils/server-rendering/utils.ts

@@ -20,26 +20,53 @@ export function isSsrRequestHandler(
   return typeof value === 'function' && '__ng_request_handler__' in value;
 }
 
+/**
+ * A mapping of the characters which have to be escaped to be interpolated into HTML,
+ * to their entity equivalents.
+ */
+const HTML_ESCAPE_CHARACTER_MAP: Record<string, string> = {
+  '&': '&amp;',
+  '<': '&lt;',
+  '>': '&gt;',
+  '"': '&quot;',
+  "'": '&#39;',
+};
+
+/**
+ * Escapes the characters of a value which is interpolated into HTML text or into a quoted
+ * attribute value.
+ *
+ * @param text - The value to escape.
+ * @returns The escaped value.
+ */
+function escapeHtml(text: string): string {
+  return text.replace(/[&<>"']/g, (character) => HTML_ESCAPE_CHARACTER_MAP[character]);
+}
+
 /**
  * Generates a static HTML page with a meta refresh tag to redirect the user to a specified URL.
  *
  * This function creates a simple HTML page that performs a redirect using a meta tag.
  * It includes a fallback link in case the meta-refresh doesn't work.
  *
+ * The provided URL is HTML-escaped before being interpolated.
+ *
  * @param url - The URL to which the page should redirect.
  * @returns The HTML content of the static redirect page.
  */
 export function generateRedirectStaticPage(url: string): string {
+  const escapedUrl = escapeHtml(url);
+
   return `
 <!DOCTYPE html>
 <html>
   <head>
     <meta charset="utf-8">
     <title>Redirecting</title>
-    <meta http-equiv="refresh" content="0; url=${url}">
+    <meta http-equiv="refresh" content="0; url=${escapedUrl}">
   </head>
   <body>
-    <pre>Redirecting to <a href="${url}">${url}</a></pre>
+    <pre>Redirecting to <a href="${escapedUrl}">${escapedUrl}</a></pre>
   </body>
 </html>
 `.trim();

packages/angular/build/src/utils/server-rendering/utils_spec.ts

@@ -0,0 +1,34 @@
+/**
+ * @license
+ * Copyright Google LLC All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.dev/license
+ */
+
+import { generateRedirectStaticPage } from './utils';
+
+describe('generateRedirectStaticPage', () => {
+  it('escapes the ampersands of a redirect target', () => {
+    const page = generateRedirectStaticPage('https://example.com/docs?from=ssg&next=/ssg');
+
+    expect(page).toContain(
+      '<meta http-equiv="refresh" content="0; url=https://example.com/docs?from=ssg&amp;next=/ssg">',
+    );
+    expect(page).toContain(
+      '<a href="https://example.com/docs?from=ssg&amp;next=/ssg">' +
+        'https://example.com/docs?from=ssg&amp;next=/ssg</a>',
+    );
+  });
+
+  it('escapes characters which would break out of the attribute or the tag', () => {
+    const page = generateRedirectStaticPage(`/"><script>alert('1')</script>`);
+
+    expect(page).not.toContain('<script>');
+    expect(page).toContain(
+      '<meta http-equiv="refresh" content="0; url=' +
+        '/&quot;&gt;&lt;script&gt;alert(&#39;1&#39;)&lt;/script&gt;">',
+    );
+    expect(page).toContain('<a href="/&quot;&gt;&lt;script&gt;alert(&#39;1&#39;)&lt;/script&gt;">');
+  });
+});

tests/legacy-cli/e2e/tests/build/server-rendering/server-routes-output-mode-static.ts

@@ -48,6 +48,10 @@ export default async function () {
       path: 'ssg-redirect',
       redirectTo: 'ssg'
     },
+    {
+      path: 'ssg-redirect-external',
+      component: Ssg,
+    },
     {
       path: 'ssg-redirect-via-guard',
       canActivate: [() => {
@@ -73,6 +77,11 @@ export default async function () {
   import { RenderMode, ServerRoute } from '@angular/ssr';
 
   export const serverRoutes: ServerRoute[] = [
+    {
+      path: 'ssg-redirect-external',
+      renderMode: RenderMode.Prerender,
+      headers: { Location: 'https://example.com/docs?from=ssg&next=/ssg' },
+    },
     {
       path: 'ssg/:id',
       renderMode: RenderMode.Prerender,
@@ -115,6 +124,9 @@ export default async function () {
     'ssg/two/index.html': /ng-server-context="ssg".+ssg-with-params works!/,
     // When static redirects are generated as meta tags.
     'ssg-redirect/index.html': '<meta http-equiv="refresh" content="0; url=/ssg">',
+    // The target of a 'Location' header is HTML escaped before it is written to the page.
+    'ssg-redirect-external/index.html':
+      '<meta http-equiv="refresh" content="0; url=https://example.com/docs?from=ssg&amp;next=/ssg">',
     'ssg-redirect-via-guard/index.html':
       '<meta http-equiv="refresh" content="0; url=/ssg?foo=bar">',
   };