# CVE-2026-49210: Symfony UX LiveComponent XSS via unvalidated child component tag

Source: https://junglewise.ai/threats/cve-2026-49210-symfony-ux-livecomponent-xss-via-unvalidated-child-component-tag  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-07-17. Updated: 2026-07-17  
License: CC BY 4.0 with a link back

CVE-2026-49210 · Severity: medium · CVSS 4 · Published 2026-07-17

Symfony UX LiveComponent, a tool used to build interactive web interfaces, contains a security flaw that could allow attackers to inject malicious scripts into a website. By sending specially crafted data to a server, an attacker could execute unauthorized code in a user's browser, potentially leading to data theft or unauthorized actions. This risk is highest for applications with specific cross-origin (CORS) configurations or those already compromised by other vulnerabilities.

Technologies: [symfony/ux-live-component (Packagist)](https://junglewise.ai/threats/technologies/symfony-ux-live-component), [Symfony UX Live Component](https://junglewise.ai/threats/technologies/ux-live-component). Vendors: [Packagist](https://junglewise.ai/threats/vendors/packagist), [Symfony](https://junglewise.ai/threats/vendors/symfony).

## Quick answers

**Is CVE-2026-49210 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-49210 being exploited in the wild.

**How severe is CVE-2026-49210?** Medium severity, with a CVSS score of 4, published 17 July 2026.

**Which products and versions are affected?** symfony/ux-live-component (Packagist) ECOSYSTEM:introduced=2.8.0,fixed=2.36.0; Symfony UX Live Component >= 2.8.0, < 2.36.0; >= 3.0.0, < 3.1.0.

**Is there a fix for CVE-2026-49210?** Yes. symfony/ux-live-component (Packagist): upgrade to 2.36.0 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-49210 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-49210?** Check whether you run symfony/ux-live-component (Packagist) or Symfony UX Live Component at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- symfony/ux-live-component (Packagist): upgrade to 2.36.0 or later

  ```sh
  composer require symfony/ux-live-component:^2.36.0
  ```


## Technical details

A Cross-Site Scripting (XSS) vulnerability exists in Symfony UX LiveComponent's ChildComponentPartialRenderer::createHtml() method. The component interpolates the client-provided 'children[id].tag' value directly into the HTML output as a tag name without proper escaping or validation. An attacker can exploit this by sending a malicious JSON payload to the Live Component endpoint, injecting arbitrary HTML or <script> tags. While default configurations require a specific 'Accept' header that mitigates cross-origin attacks, the vulnerability is exploitable if CORS policies are overly permissive or if the attacker has achieved a same-origin pivot. The issue is resolved in versions 2.36.0 and 3.1.0 by implementing a strict regex validation for HTML tag names.

## Affected products

- Symfony ux-live-component >= 2.8.0, < 2.36.0; >= 3.0.0, < 3.1.0

## Identifiers

- CVE-2026-49210
- GHSA-38x5-rcv4-xf7x

## Timeline

- 2026-05-29: patched: Fixed in versions 2.36.0 and 3.1.0
- 2026-05-29: advisory: GitHub Security Advisory published
- 2026-07-17: disclosed: CVE published to NVD

## References

- [https://github.com/symfony/ux/commit/fbc5e9a1bda7e4556be21bb1d970f382760ed9a9](https://github.com/symfony/ux/commit/fbc5e9a1bda7e4556be21bb1d970f382760ed9a9)
- [https://github.com/symfony/ux/releases/tag/v2.36.0](https://github.com/symfony/ux/releases/tag/v2.36.0)
- [https://github.com/symfony/ux/releases/tag/v3.1.0](https://github.com/symfony/ux/releases/tag/v3.1.0)
- [https://github.com/symfony/ux/security/advisories/GHSA-38x5-rcv4-xf7x](https://github.com/symfony/ux/security/advisories/GHSA-38x5-rcv4-xf7x)

## Related threats

- [Symfony UX LiveComponent CSRF in LiveAction invocations](https://junglewise.ai/threats/cve-2026-49215-symfony-ux-livecomponent-csrf-in-liveaction-invocations)
- [Symfony UX insufficient verification of data authenticity in LiveComponent](https://junglewise.ai/threats/cve-2026-49212-symfony-ux-insufficient-verification-of-data-authenticity-in)
- [Symfony UX LiveComponent denial of service in BatchActionController](https://junglewise.ai/threats/cve-2026-49209-symfony-ux-livecomponent-denial-of-service-in)
- [Symfony UX LiveComponent improper input validation in date hydration](https://junglewise.ai/threats/cve-2026-49208-symfony-ux-livecomponent-improper-input-validation-in-date)
- [Symfony UX allows unsanitized HTML attribute injection via ComponentAttributes](https://junglewise.ai/threats/cve-2025-47946-symfony-ux-allows-unsanitized-html-attribute-injection-via)