symfony/ux-live-component: CSRF Protection Bypass — Accept Header is CORS-Safelisted
Date: 2026-06
Affected: composer/symfony/ux-live-component, composer/symfony/ux-live-component
Attack vector: other
Category: vulnerability-disclosure
Severity: Low
CVE: CVE-2026-49215
CWE: CWE-352

### Description When using `symfony/ux-live-component`, methods annotated with `#[LiveAction]` are invokable from the browser and mutate server-side state via AJAX. `Symfony\UX\LiveComponent\EventListener\LiveComponentSubscriber::isLiveComponentRequest()` gated these invocations on the presence of `Accept: application/vnd.live-component+html`, with a code comment stating that this acted as a CSRF protection. The `Accept` header is a [CORS-safelisted request header](https://fetch.spec.whatwg.org/#cors-safelisted-request-header), so a cross-origin `fetch()` can set it without triggering a preflight. The header therefore provided no CSRF protection. Any `#[LiveAction]` could be forged cross-origin against a victim's session. In practice the attack is mitigated by `SameSite=Lax` session cookies (Symfony's default), but applications using `SameSite=None`, `credentials: 'include'` with a permissive cookie policy, or that have been pivoted from another same-origin vector remained exposed. ### Resolution `isLiveComponentRequest()` now additionally requires the request header `X-Requested-With: XMLHttpRequest`. This header is **not** CORS-safelisted, so the browser issues a preflight `OPTIONS` request for any cross-origin attempt; Symfony does not advertise CORS for LiveComponent endpoints, the preflight fails, and the real request is blocked before it reaches the application. The bundled Stimulus client already sends `X-Requested-With` on every LiveComponent request (`RequestBui


Mitigations:

Architectural layers (MAESTRO):