GHSA-38X5-RCV4-XF7X

Vulnerability from github – Published: 2026-06-19 19:34 – Updated: 2026-06-19 19:34
VLAI
Summary
symfony/ux-live-component: XSS via attacker-controlled child component tag
Details

Description

Symfony\UX\LiveComponent\Util\ChildComponentPartialRenderer::createHtml() interpolates the $childTag argument directly into the HTML output as a tag name, without escaping or validation. The value originates from client-controlled JSON (children[id].tag) parsed by LiveComponentSubscriber and propagated through InterceptChildComponentRenderSubscriber, so an attacker who can reach the Live Component endpoint can inject arbitrary HTML, including <script> tags, on any re-render of a Live Component that contains at least one child component.

In the default configuration, the Live Component endpoint is gated by an Accept: application/vnd.live-component+html request-header check that cannot be set cross-origin without a CORS preflight, so the issue is primarily a defense-in-depth gap. It becomes directly exploitable on applications that have relaxed CORS to allow this header from untrusted origins, or that have been pivoted from another same-origin XSS.

Resolution

ChildComponentPartialRenderer now validates $childTag against a strict HTML tag-name regex before interpolating it, and rejects any value that doesn't match. Anything that wouldn't be a valid HTML tag is dropped before reaching the response.

The patch for this issue is available here for branch 2.x (and forward-ported to 3.x).

Credits

Symfony would like to thank Pascal Cescon for reporting the issue and Hugo Alliaume for providing the fix.

Severity
5.1 (Medium)
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:N/VI:N/VA:N/SC:L/SI:L/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-2026-49210"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-79"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-06-19T19:34:49Z",
    "nvd_published_at": null,
    "severity": "MODERATE"
  },
  "details": "### Description\n\n`Symfony\\UX\\LiveComponent\\Util\\ChildComponentPartialRenderer::createHtml()` interpolates the `$childTag` argument directly into the HTML output as a tag name, without escaping or validation. The value originates from client-controlled JSON (`children[id].tag`) parsed by `LiveComponentSubscriber` and propagated through `InterceptChildComponentRenderSubscriber`, so an attacker who can reach the Live Component endpoint can inject arbitrary HTML, including `\u003cscript\u003e` tags, on any re-render of a Live Component that contains at least one child component.\n\nIn the default configuration, the Live Component endpoint is gated by an `Accept: application/vnd.live-component+html` request-header check that cannot be set cross-origin without a CORS preflight, so the issue is primarily a defense-in-depth gap. It becomes directly exploitable on applications that have relaxed CORS to allow this header from untrusted origins, or that have been pivoted from another same-origin XSS.\n\n### Resolution\n\n`ChildComponentPartialRenderer` now validates `$childTag` against a strict HTML tag-name regex before interpolating it, and rejects any value that doesn\u0027t match. Anything that wouldn\u0027t be a valid HTML tag is dropped before reaching the response.\n\nThe patch for this issue is available [here](https://github.com/symfony/ux/commit/fbc5e9a1bda7e4556be21bb1d970f382760ed9a9) for branch 2.x (and forward-ported to 3.x).\n\n### Credits\n\nSymfony would like to thank Pascal Cescon for reporting the issue and Hugo Alliaume for providing the fix.",
  "id": "GHSA-38x5-rcv4-xf7x",
  "modified": "2026-06-19T19:34:49Z",
  "published": "2026-06-19T19:34:49Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/symfony/ux/security/advisories/GHSA-38x5-rcv4-xf7x"
    },
    {
      "type": "WEB",
      "url": "https://github.com/symfony/ux/commit/fbc5e9a1bda7e4556be21bb1d970f382760ed9a9"
    },
    {
      "type": "WEB",
      "url": "https://github.com/FriendsOfPHP/security-advisories/blob/master/symfony/ux-live-component/CVE-2026-49210.yaml"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/symfony/ux"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N",
      "type": "CVSS_V4"
    }
  ],
  "summary": "symfony/ux-live-component: XSS via attacker-controlled child component tag"
}



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