CVE-2026-49212Low▾ Sunlitsymfony/ux-live-component: LiveComponentHydrator HMAC checksum lacks component and slot binding
▾ Sunlit zone — Low / medium · no exploitation signal
impact 13.8 · likelihood 0 · exploitation 0
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Exploit-prediction probability, daily snapshots since Jul 18.
Disclosure to exploitation, from the record and what we observed since indexing it.
Disclosed via GHSA
0.2%
0.2% → 0.2%
In symfony/ux-live-component, a component's server-side state is exposed to the browser as a set of props (#[LiveProp]-annotated properties). Props marked writable: true can be freely changed by the client. Read-only props are round-tripped to the browser and back, and their integrity is protected by an HMAC so the client cannot tamper with them. Child components additionally receive a propsFromParent blob, also HMAC-signed.
The HMAC computed by Symfony\UX\LiveComponent\LiveComponentHydrator covered only the sorted prop key/value pairs. It didn't include the component name, the slot identifier (props vs propsFromParent), or any request context, and a single application-wide secret is used for every component. A signed blob the server minted for component A is therefore a valid signature for component B if the key names happen to match, and a props blob can be replayed in the propsFromParent slot (or the reverse). An attacker can use this to set a read-only prop on a target component to a value they were only ever allowed to choose as a writable prop on another component.
The HMAC is now bound to its context: the component name and a slot identifier are included in the pre-image before hashing. Two constants (CHECKSUM_SLOT_PROPS and CHECKSUM_SLOT_PROPS_FROM_PARENT) name the two slots, and calculateChecksum(), verifyChecksum(), addChecksumToData(), and ChildComponentPartialRenderer thread these values through. Cross-component and cross-slot replays no longer verify.
The patch for this issue is available here for branch 2.x (and forward-ported to 3.x).
Symfony would like to thank Anthropic (via Project Glasswing) for reporting the issue and Hugo Alliaume for providing the fix.
symfony/ux-live-component >= 2.8.0, < 2.36.0symfony/ux-live-component >= 3.0.0, < 3.1.0Upgrade to a patched release:
symfony/ux-live-component 2.36.0symfony/ux-live-component 3.1.0Connected by shared product, vendor, weakness, or advisory.
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