{"id":"GHSA-38x5-rcv4-xf7x","summary":"symfony/ux-live-component: XSS via attacker-controlled child component tag","details":"### Description\n\n`Symfony\\UX\\LiveComponent\\Util\\ChildComponentPartialRenderer::createHtml()` interpolates the `$childTag` argument directly into the HTML output as a tag name, without escaping or validation. The value originates from client-controlled JSON (`children[id].tag`) parsed by `LiveComponentSubscriber` and propagated through `InterceptChildComponentRenderSubscriber`, so an attacker who can reach the Live Component endpoint can inject arbitrary HTML, including `\u003cscript\u003e` tags, on any re-render of a Live Component that contains at least one child component.\n\nIn the default configuration, the Live Component endpoint is gated by an `Accept: application/vnd.live-component+html` request-header check that cannot be set cross-origin without a CORS preflight, so the issue is primarily a defense-in-depth gap. It becomes directly exploitable on applications that have relaxed CORS to allow this header from untrusted origins, or that have been pivoted from another same-origin XSS.\n\n### Resolution\n\n`ChildComponentPartialRenderer` now validates `$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.","aliases":["CVE-2026-49210"],"modified":"2026-09-10T03:51:07.753980491Z","published":"2026-06-19T19:34:49Z","database_specific":{"github_reviewed":true,"github_reviewed_at":"2026-06-19T19:34:49Z","nvd_published_at":null,"cwe_ids":["CWE-79"],"severity":"MODERATE"},"references":[{"type":"WEB","url":"https://github.com/symfony/ux/security/advisories/GHSA-38x5-rcv4-xf7x"},{"type":"WEB","url":"https://github.com/symfony/ux/commit/fbc5e9a1bda7e4556be21bb1d970f382760ed9a9"},{"type":"WEB","url":"https://github.com/FriendsOfPHP/security-advisories/blob/master/symfony/ux-live-component/CVE-2026-49210.yaml"},{"type":"PACKAGE","url":"https://github.com/symfony/ux"}],"affected":[{"package":{"name":"symfony/ux-live-component","ecosystem":"Packagist","purl":"pkg:composer/symfony/ux-live-component"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"2.8.0"},{"fixed":"2.36.0"}]}],"versions":["v2.10.0","v2.11.0","v2.11.1","v2.11.2","v2.12.0","v2.13.0","v2.13.1","v2.13.2","v2.13.3","v2.14.0","v2.14.1","v2.14.2","v2.15.0","v2.16.0","v2.17.0","v2.18.0","v2.18.1","v2.19.0","v2.19.2","v2.20.0","v2.21.0","v2.22.0","v2.22.1","v2.23.0","v2.24.0","v2.25.0","v2.25.1","v2.25.2","v2.26.0","v2.26.1","v2.27.0","v2.28.0","v2.28.1","v2.28.2","v2.29.0","v2.29.1","v2.29.2","v2.30.0","v2.31.0","v2.32.0","v2.33.0","v2.34.0","v2.35.0","v2.8.0","v2.8.1","v2.9.0","v2.9.1"],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/06/GHSA-38x5-rcv4-xf7x/GHSA-38x5-rcv4-xf7x.json"}},{"package":{"name":"symfony/ux-live-component","ecosystem":"Packagist","purl":"pkg:composer/symfony/ux-live-component"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"3.0.0"},{"fixed":"3.1.0"}]}],"versions":["v3.0.0"],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/06/GHSA-38x5-rcv4-xf7x/GHSA-38x5-rcv4-xf7x.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V4","score":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N"}]}