Description
A Cross-Site Scripting (XSS) vulnerability exists in `@angular/platform-server`'s DOM emulation dependency (`domino`) when serializing the content of `<noscript>` elements.
When rendering dynamic text content inside a `<noscript>` element via template bindings (such as `{{ value }}` or `[textContent]`), the template engine expects the browser to render the content safely. Under Server-Side Rendering (SSR), `domino` is configured with scripting enabled, meaning `<noscript>` is treated as a raw-text element.
However, `domino`'s serializer completely omitted `<noscript>` from the list of raw-text elements requiring closing-tag escaping during DOM serialization. As a result, any occurrence of `</noscript>` in the bound dynamic text was **never escaped under any circumstances**.
The unescaped closing tag was serialized directly into the output HTML (e.g. `<noscript></noscript><script>alert(1)</script></noscript>`). When parsed by a browser, it closes the `<noscript>` block early, allowing the 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 a `<noscript>` element. This can lead to session hijacking, credentials theft, unauthorized actions on behalf of users, and defacement.
### Patched Versions
- 22.0.0-rc.2
- 21.2.16
- 20.3.24
- 19.2.25
### Workarounds
If you cannot immediately update your dependencies, you can:
- Avoid binding user-controlled values inside `<noscript>` elements.
- Sanitize any user input placed inside `<noscript>` to explicitly strip closing `</noscript>` tags before passing it to the template.