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GHSA-34W5-C283-J9FG

Vulnerability from github – Published: 2026-06-19 19:34 – Updated: 2026-06-19 19:34
VLAI
Summary
symfony/ux-live-component: LiveComponentHydrator HMAC checksum lacks component and slot binding
Details

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

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

Severity
2.3 (Low)
CVSS:4.0/AV:N/AC:H/AT:N/PR:L/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N
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{
  "affected": [
    {
      "package": {
        "ecosystem": "Packagist",
        "name": "symfony/ux-live-component"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "2.8.0"
            },
            {
              "fixed": "2.36.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "Packagist",
        "name": "symfony/ux-live-component"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "3.0.0"
            },
            {
              "fixed": "3.1.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-49212"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-345"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-06-19T19:34:56Z",
    "nvd_published_at": null,
    "severity": "LOW"
  },
  "details": "### Description\n\nIn `symfony/ux-live-component`, a component\u0027s 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.\n\nThe HMAC computed by `Symfony\\UX\\LiveComponent\\LiveComponentHydrator` covered only the sorted prop key/value pairs. It didn\u0027t 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.\n\n### Resolution\n\nThe 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.\n\nThe patch for this issue is available [here](https://github.com/symfony/ux/commit/a224b5af3e2e33ee14ac71356ae0e0877900a81c) for branch 2.x (and forward-ported to 3.x).\n\n### Credits\n\nSymfony would like to thank Anthropic (via Project Glasswing) for reporting the issue and Hugo Alliaume for providing the fix.",
  "id": "GHSA-34w5-c283-j9fg",
  "modified": "2026-06-19T19:34:56Z",
  "published": "2026-06-19T19:34:56Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/symfony/ux/security/advisories/GHSA-34w5-c283-j9fg"
    },
    {
      "type": "WEB",
      "url": "https://github.com/symfony/ux/commit/a224b5af3e2e33ee14ac71356ae0e0877900a81c"
    },
    {
      "type": "WEB",
      "url": "https://github.com/FriendsOfPHP/security-advisories/blob/master/symfony/ux-live-component/CVE-2026-49212.yaml"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/symfony/ux"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:H/AT:N/PR:L/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N",
      "type": "CVSS_V4"
    }
  ],
  "summary": "symfony/ux-live-component: LiveComponentHydrator HMAC checksum lacks component and slot binding"
}



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