XSS in Symfony Ux
CVE-2026-49210
Symfony UX is a JavaScript ecosystem for Symfony. From 2.8.0 until 2.36.0 and 3.1.0, Symfony\UX\LiveComponent\Util\ChildComponentPartialRenderer::createHtml() interpolates the client-controlled children[id].tag value from LiveComponentSubscriber and InterceptChildComponentRenderSubscriber directly into HTML as a tag name without escaping or validation, allowing arbitrary HTML, including <script> tags, on any Live Component re-render that contains at least one child component. This issue is fixed in versions 2.36.0 and 3.1.0.
Vulnerability class: XSS (Cross-Site Scripting)
EPSS: 0.003 (26.4th percentile) — read the EPSS interpretation.
CVSS v3 metric
CVSS v3 base score 6.1 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N.
Affected products
- Symfony Ux — versions >= 2.8.0, < 2.36.0, >= 3.0.0, < 3.1.0, 3.0.0
Weakness classification (CWE)
References
- security-advisories@github.com (x_refsource_CONFIRM, Vendor Advisory)
- security-advisories@github.com (Patch, x_refsource_MISC)
- security-advisories@github.com (x_refsource_MISC, Release Notes)
- security-advisories@github.com (x_refsource_MISC, Release Notes)
Frequently asked questions
- What is CVE-2026-49210?
- CVE-2026-49210 is a medium-severity vulnerability in Symfony Ux, classified under Cross-site Scripting. CVSS score: 6.1/10. Published 2026-07-17.
- How severe is CVE-2026-49210?
- Medium severity. CVSS v3 base score is 6.1 out of 10.