{"schema":"threatline.record/2","record":{"id":"CVE-2026-102989","aliases":["GHSA-qx66-fv34-fjm8"],"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.","categories":["Libraries & packages"],"product":"@tanstack/start-server-core","vendor":"TanStack","ecosystem":"npm","affected_ranges":[{"source":"GitHub Advisory Database","source_url":"https://github.com/advisories/GHSA-qx66-fv34-fjm8","source_modified_at":"2026-10-15T20:22:22Z","fetched_at":"2026-10-23T18:42:43.628194Z","package":{"ecosystem":"npm","name":"@tanstack/start-server-core"},"range":">= 1.143.12, < 1.169.39"},{"source":"GitHub Advisory Database","source_url":"https://github.com/advisories/GHSA-qx66-fv34-fjm8","source_modified_at":"2026-10-15T20:22:22Z","fetched_at":"2026-10-23T18:42:43.628194Z","package":{"ecosystem":"npm","name":"@tanstack/react-start"},"range":">= 1.143.12, < 1.168.60"},{"source":"GitHub Advisory 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