🛡️ CVE-2026-49210 — ux

🟡 CVSS 6.1 — Medium ✅ No Known Exploit CWE-79 NVD
6.1
CVSS Score
0 Low4 Medium7 High9 Critical10

Description

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

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](https://github.com/symfony/ux/commit/fbc5e9a1bda7e4556be21bb1d970f382760ed9a9) 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.

How this vulnerability can be exploited

This issue can be reached over the network, attack complexity is low, an attacker needs no privileges on the target. A user must be tricked into taking some action. The scope is changed, meaning a successful attack can affect components beyond the vulnerable one. Rated impact: confidentiality low, integrity low, availability none.

Weakness class

CVE-2026-49210 is classified as CWE-79: Cross-site Scripting (XSS). User-supplied data is written into a page without escaping, so attacker script runs in the browser of anyone who views it.

Affected software

CVE-2026-49210 is recorded against 2 packages.

  • symfony/ux-live-component (from 3.0.0 up to 3.1.0)
  • ux

Timeline and source

Published on 19 June 2026. No public exploit is currently recorded for this entry. A vendor advisory or fix has been published. Record sourced from NVD.

References

github.com (Web)
github.com (Web)
github.com (Web)
github.com (Package)

Details

Severity Medium
CVSS Score 6.1
CVSS Vector CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
CWE CWE-79
Public Exploit ✅ No
Source NVD
Published 2026-06-19
Updated 2026-08-12
Modified 2026-06-19

Affected Packages

Software From version Fixed in
symfony/ux-live-component 3.0.0 3.1.0
ux — —

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