A Cross-Site Scripting (XSS) vulnerability exists in @angular/platform-server's DOM emulation dependency (domino) when serializing the content of `` elements.
When rendering dynamic text content inside a ` 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 ` is treated as a raw-text element.
However, domino's serializer completely omitted ` from the list of raw-text elements requiring closing-tag escaping during DOM serialization. As a result, any occurrence of ` in the bound dynamic text was never escaped under any circumstances.
The unescaped closing tag was serialized directly into the output HTML (e.g. `). When parsed by a browser, it closes the block early, allowing the injected ` 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 `` 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 `` elements.
- Sanitize any user input placed inside `
to explicitly strip closing ` tags before passing it to the template.
