{"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":0.27227,"slug":"CVE-2026-49210","body":"## Overview\n\n### Description\n\n`Symfony\\UX\\LiveComponent\\Util\\ChildComponentPartialRenderer::createHtml()` interpolates the `$childTag` argument directly into the HTML output as a tag name, without escaping or validation. The value originates from client-controlled JSON (`children[id].tag`) parsed by `LiveComponentSubscriber` and propagated through `InterceptChildComponentRenderSubscriber`, so an attacker who can reach the Live Component endpoint can inject arbitrary HTML, including `<script>` tags, on any re-render of a Live Component that contains at least one child component.\n\nIn the default configuration, the Live Component endpoint is gated by an `Accept: application/vnd.live-component+html` request-header check that cannot be set cross-origin without a CORS preflight, so the issue is primarily a defense-in-depth gap. It becomes directly exploitable on applications that have relaxed CORS to allow this header from untrusted origins, or that have been pivoted from another same-origin XSS.\n\n### Resolution\n\n`ChildComponentPartialRenderer` now validates `$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.\n\nThe patch for this issue is available [here](https://github.com/symfony/ux/commit/fbc5e9a1bda7e4556be21bb1d970f382760ed9a9) for branch 2.x (and forward-ported to 3.x).\n\n### Credits\n\nSymfony would like to thank Pascal Cescon for reporting the issue and Hugo Alliaume for providing the fix.\n\n## Affected packages\n\n- `symfony/ux-live-component >= 2.8.0, < 2.36.0`\n- `symfony/ux-live-component >= 3.0.0, < 3.1.0`\n\n## Remediation\n\nUpgrade to a patched release:\n\n- `symfony/ux-live-component 2.36.0`\n- `symfony/ux-live-component 3.1.0`","depth":"sunlit","depthScore":28,"depthScoreParts":{"impact":27.5,"likelihood":0.1,"exploitation":0,"ransomware":0},"changes":[]}