All vulnerabilities
CVE-2026-102989GHSA-qx66-fv34-fjm8

@tanstack/start-server-core: TanStack Router: Unauthenticated reflected XSS in TanStack Start server-function responses

TanStack @tanstack/start-server-corenpmLibraries & packages
Open in ThreatlineRecord JSON
CVSS
9.3Critical
ExploitationNo known exploitationNot in CISA KEV, which does not prove it is unexploitedCISA KEV
Exploit odds (EPSS)0.52%Chance of exploitation activity in the next 30 days, higher than 43% of CVEs. Scored 23 Oct 2026FIRST EPSS
Fixed in1.169.39Also 1.168.60, 1.168.57 and 1 moreGitHub
Published13 Oct 2026Updated 15 Oct 2026CVE List

What fixes it

  • 1.169.39@tanstack/start-server-core, npmGitHubnpm install @tanstack/start-server-core@1.169.39
  • 1.168.60@tanstack/react-start, npmGitHubnpm install @tanstack/react-start@1.168.60
  • 1.168.57@tanstack/solid-start, npmGitHubnpm install @tanstack/solid-start@1.168.57
  • 1.168.56@tanstack/vue-start, npmGitHubnpm install @tanstack/vue-start@1.168.56

A fixed version on one release line is not the upgrade target for every line. Check your exact version and any vendor backports.

Timeline

  1. 12 Oct 2026, 00:00 UTCWAF rule availableCloudflare WAF
  2. 13 Oct 2026, 16:13 UTCPublishedCVE List

Protection while you patch 1

WAF and edge providers that shipped rules for this CVE. A rule can block known attack patterns; it does not fix the software, so still upgrade.

Reports 1

1 outlet mention it. Reports are not confirmation; each links to its source.

Description

Impact

An 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.

Cause

The 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.

Affected versions

Published 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.

Fix

The fix limits client-supplied server-function input to public fields and validates responses at the server boundary. Upgrade to the corresponding patched package version.

Temporary mitigations

For 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.

Credits

Lovable helped us discover and report this issue. We thank them for their help.

Text from GitHub Advisory Database

Affected versions 13

  • @tanstack/start-server-core, npm>= 1.143.12, < 1.169.39GitHub
  • @tanstack/react-start, npm>= 1.143.12, < 1.168.60GitHub
  • @tanstack/solid-start, npm>= 1.143.12, < 1.168.57GitHub
  • @tanstack/vue-start, npm>= 1.143.12, < 1.168.56GitHub
  • routeraffected: < release-2026-09-30-1747CVE List
  • react-startaffected: >= 1.143.12, < 1.168.60CVE List
  • solid-startaffected: >= 1.143.12, < 1.168.57CVE List
  • start-server-coreaffected: >= 1.143.12, < 1.169.39CVE List
  • vue-startaffected: >= 1.143.12, < 1.168.56CVE List
  • @tanstack/start-server-core, npmfrom 1.143.12, fixed in 1.169.39OSV
  • @tanstack/react-start, npmfrom 1.143.12, fixed in 1.168.60OSV
  • @tanstack/solid-start, npmfrom 1.143.12, fixed in 1.168.57OSV
  • @tanstack/vue-start, npmfrom 1.143.12, fixed in 1.168.56OSV

References 6