symfony/ux-live-component: XSS via attacker-controlled child component tag

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

5.1 · 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 · score source

EPSS

• CVE-2026-49210: 0.34% estimated exploitation activity in the next 30 days; percentile 27.27 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

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…

Published by the source

19 Jun 2026, 19:34 UTC

Last modified by the source

19 Jun 2026, 19:34 UTC

Source last checked

26 Oct 2026, 14:49 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-38x5-rcv4-xf7x

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# Patch Next advisory brief: CVE-2026-49210

Advisory: symfony/ux-live-component: XSS via attacker-controlled child component tag
IDs: CVE-2026-49210, GHSA-38x5-rcv4-xf7x
Record: https://patchnext.com/advisories/cve-2026-49210 (revision 1, source checked 26 Oct 2026, 14:49 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.1)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: symfony/ux-live-component 3.1.0, 2.36.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- Packagist symfony/ux-live-component: affected >= 2.8.0, < 2.36.0; >= 3.0.0, < 3.1.0; fixed in 3.1.0, 2.36.0

## Suggested inspection (read-only)
- Packagist symfony/ux-live-component: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on symfony/ux-live-component.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-38x5-rcv4-xf7x (GitHub-reviewed advisory GHSA-38x5-rcv4-xf7x lists affected ranges: Packagist symfony/ux-live-component >=2.8.0 =3.0.0 <3.1.0)

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