---
id: CVE-2026-49212
title: >-
  symfony/ux-live-component: LiveComponentHydrator HMAC checksum lacks component
  and slot binding
summary: >-
  symfony/ux-live-component: LiveComponentHydrator HMAC checksum lacks component
  and slot binding
severity: low
cwe:
  - CWE-345
vendor: symfony
product: symfony/ux-live-component
affected:
  - 'symfony/ux-live-component >= 2.8.0, < 2.36.0'
  - 'symfony/ux-live-component >= 3.0.0, < 3.1.0'
patched:
  - symfony/ux-live-component 2.36.0
  - symfony/ux-live-component 3.1.0
published: '2026-06-19'
updated: '2026-06-19'
source: GHSA
sourceUrl: 'https://github.com/advisories/GHSA-34w5-c283-j9fg'
references:
  - url: 'https://github.com/symfony/ux/security/advisories/GHSA-34w5-c283-j9fg'
  - url: >-
      https://github.com/symfony/ux/commit/a224b5af3e2e33ee14ac71356ae0e0877900a81c
  - url: >-
      https://github.com/FriendsOfPHP/security-advisories/blob/master/symfony/ux-live-component/CVE-2026-49212.yaml
  - url: 'https://github.com/advisories/GHSA-34w5-c283-j9fg'
tags:
  - ghsa
  - composer
ingestedAt: '2026-06-22T15:52:21.063Z'
ecosystem: composer
epss: 0.00242
epssPercentile: 0.13674
---

## Overview

### 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](https://github.com/symfony/ux/commit/a224b5af3e2e33ee14ac71356ae0e0877900a81c) for branch 2.x (and forward-ported to 3.x).

### Credits

Symfony would like to thank Anthropic (via Project Glasswing) for reporting the issue and Hugo Alliaume for providing the fix.

## Affected packages

- `symfony/ux-live-component >= 2.8.0, < 2.36.0`
- `symfony/ux-live-component >= 3.0.0, < 3.1.0`

## Remediation

Upgrade to a patched release:

- `symfony/ux-live-component 2.36.0`
- `symfony/ux-live-component 3.1.0`