{"id":"CVE-2026-102989","aliases":["GHSA-qx66-fv34-fjm8"],"url":"https://o3.security/vulnerability/CVE-2026-102989","summary":"TanStack Router: Unauthenticated reflected XSS in TanStack Start server-function responses","details":"## Impact\n\nAn unauthenticated attacker can craft a URL to a server function in an affected TanStack Start app. If someone opens the link, the app can return attacker-controlled HTML from its own origin and run the attacker's JavaScript there. The script can access same-origin data available to that visitor and make requests with their authority.\n\n## Cause\n\nThe server-function transport can pass request payload fields into internal middleware state instead of limiting them to public input fields. A malformed payload can leave an attacker-controlled result in the error path. Response handling can then treat a response-shaped object as an HTTP response.\n\n## Affected versions\n\nPublished versions of `@tanstack/start-server-core`, `@tanstack/react-start`, `@tanstack/solid-start`, and `@tanstack/vue-start` from `1.143.12` up to, but not including, their respective patched versions are affected. The patched versions are `@tanstack/start-server-core@1.169.39`, `@tanstack/react-start@1.168.60`, `@tanstack/solid-start@1.168.57`, and `@tanstack/vue-start@1.168.56`.\n\n## Fix\n\nThe fix limits client-supplied server-function input to public fields and validates responses at the server boundary. Upgrade to the corresponding patched package version.\n\n## Temporary mitigations\n\nFor the configured server-function path, usually `/_serverFn/*`, an edge or WAF rule can consider blocking requests without the literal `x-tsr-serverFn: true` header and browser document navigations such as `Sec-Fetch-Mode: navigate` or `Accept: text/html`. A restrictive Content Security Policy on server-function responses can provide another browser-side restriction. These are mitigation suggestions, not a complete fix. The header is client-controlled and is not authentication. Test rules against legitimate GET and POST server functions and use a matching version-specific backport where possible.\n\n## Credits\n\nLovable helped us discover and report this issue. We thank them for their help.","published":"2026-10-13T16:13:13.105Z","modified":"2026-10-21T02:54:32.007338411Z","cvss":{"score":9.3,"severity":"CRITICAL","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:N"},"epss":null,"cisaKev":null,"exploitsKnown":null,"affectedPackages":[{"ecosystem":"npm","name":"@tanstack/start-server-core","fixedVersion":"1.169.39"},{"ecosystem":"npm","name":"@tanstack/react-start","fixedVersion":"1.168.60"},{"ecosystem":"npm","name":"@tanstack/solid-start","fixedVersion":"1.168.57"},{"ecosystem":"npm","name":"@tanstack/vue-start","fixedVersion":"1.168.56"}],"fix":{"url":"https://github.com/TanStack/router/commit/d521abd71c69f1ff010bb3def4d417cb5fa058cb","label":"TanStack/router@d521abd"},"references":[{"type":"WEB","url":"https://github.com/TanStack/router/releases/tag/release-2026-09-30-1747"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/102xxx/CVE-2026-102989.json"},{"type":"ADVISORY","url":"https://github.com/TanStack/router/security/advisories/GHSA-qx66-fv34-fjm8"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-102989"},{"type":"FIX","url":"https://github.com/TanStack/router/commit/d521abd71c69f1ff010bb3def4d417cb5fa058cb"},{"type":"FIX","url":"https://github.com/TanStack/router/pull/8573"},{"type":"PACKAGE","url":"https://github.com/TanStack/router"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-10-21T02:54:32.007338411Z"}}