---
id: CVE-2026-49210
title: 'symfony/ux-live-component: XSS via attacker-controlled child component tag'
summary: 'symfony/ux-live-component: XSS via attacker-controlled child component tag'
severity: medium
cwe:
  - CWE-79
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-38x5-rcv4-xf7x'
references:
  - url: 'https://github.com/symfony/ux/security/advisories/GHSA-38x5-rcv4-xf7x'
  - url: >-
      https://github.com/symfony/ux/commit/fbc5e9a1bda7e4556be21bb1d970f382760ed9a9
  - url: >-
      https://github.com/FriendsOfPHP/security-advisories/blob/master/symfony/ux-live-component/CVE-2026-49210.yaml
  - url: 'https://github.com/advisories/GHSA-38x5-rcv4-xf7x'
tags:
  - ghsa
  - composer
ingestedAt: '2026-06-22T15:52:21.066Z'
ecosystem: composer
epss: 0.00338
epssPercentile: 0.24425
---

## Overview

### 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.

## 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`