Affected versions
Symfony versions >=2.8.0, <2.36.0, >=3.0.0, <3.1.0 of the Symfony UX Live Component component are affected by this security issue.
The issue has been fixed in Symfony 2.36.0, 3.1.0.
Description
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.
Resolution
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).
Credits
We would like to thank Anthropic (via Project Glasswing) for reporting the issue and Hugo Alliaume for providing the fix.