GHSA-vpx6-8pjr-4g3v Angular SSR: Missing Fallback Raw-Content Serialization Escaping leads to Cross-Site Scripting (XSS)

• npm @angular/platform-server: >= 22.0.0-next.0, < 22.0.7 → fixed in 22.0.7 • npm @angular/platform-server: >= 21.0.0-next.0, < 21.2.19 → fixed in 21.2.19 • npm @angular/platform-server: >= 20.0.0-next.0, < 20.3.27 → fixed in 20.3.27 • npm @angular/platform-server: <= 19.2.25 (no fix yet)

A Cross-Site Scripting (XSS) vulnerability exists in `@angular/platform-server`'s DOM emulation dependency (`domino`) when serializing the content of fallback raw-content elements (``, ``, ``, and ``). When rendering dynamic text content inside fallback raw-content elements via template bindings, the template engine expects the browser to render the content safely. Under Server-Side Rendering (SSR), `domino` is configured with scripting enabled, meaning these elements are treated as raw-text elements. However, `domino`'s serializer previously did not escape text nodes within fallback raw-content elements (``, ``, ``, ``) during DOM serialization. As a result, any occurrence of closing tags in the bound dynamic text was not escaped. The unescaped closing tag could be serialized directly into the output HTML. When parsed by a browser or re-parsed during SSR post-processing without preserving raw-content parser state, an injected closing tag closes the element early, allowing an injected script block to execute in the user's browser context, causing same-origin Cross-Site Scripting (XSS). Impact This vulnerability allows an attacker to perform same-origin Cross-Site Scripting (XSS) attacks against any user visiting an SSR-rendered page that binds user-controlled data inside fallback raw-content elements (``, ``, ``, ``). This can lead to session hijacking, credentials theft, unauthorized actions on behalf of users, and defacement. Patched Versions • 22.0.7 • 21.2.19 • 20.3.27 Workarounds If you cannot immediately update your dependencies, you can mitigate this issue using any of the following approaches: • Disable critical CSS inlining: Critical CSS inlining in Angular SSR post-processes the rendered HTML using `domino`. Disabling this step prevents `domino` from re-parsing and re-serializing the HTML during server-side rendering. • In `angular.json`, set `inlineCritical` to `false` under style optimization options: ```json { "projects": { "my-app": { "architect": { "build": { "builder": "@angular/build:application", "options": { "optimization": { "styles": { "inlineCritical": false } } } } } } } } ``` • When rendering programmatically with `CommonEngine`, set `inlineCriticalCss: false` in your render options. • Avoid binding user-controlled values inside fallback raw-content elements (``, ``, ``, ``). • Sanitize user input placed inside these elements to explicitly strip or escape closing tags before passing it to the template.