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Critical, CVSS 9.3amended

TanStack Router: Unauthenticated reflected XSS in TanStack Start server-function responses

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

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (@tanstack/start-server-core 1.169.39; @tanstack/vue-start 1.168.56; @tanstack/solid-start 1.168.57; @tanstack/react-start 1.168.60), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS
9.3 · CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:N
EPSS
  • CVE-2026-102989: 0.54% estimated exploitation activity in the next 30 days; percentile 45.71 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

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,…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 3 · amended ·

    Amended from ghsa record GHSA-qx66-fv34-fjm8

  2. Revision 2 · amended ·

    Amended from osv record GHSA-qx66-fv34-fjm8

  3. Revision 1 · created ·

    Published from ghsa record GHSA-qx66-fv34-fjm8

Agent brief

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# Patch Next advisory brief: CVE-2026-102989

Advisory: TanStack Router: Unauthenticated reflected XSS in TanStack Start server-function responses
IDs: CVE-2026-102989, GHSA-qx66-fv34-fjm8
Record: https://patchnext.com/advisories/cve-2026-102989 (revision 3, source checked 26 Oct 2026, 13:07 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Critical (CVSS 9.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: @tanstack/start-server-core 1.169.39; @tanstack/vue-start 1.168.56; @tanstack/solid-start 1.168.57; @tanstack/react-start 1.168.60. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm @tanstack/start-server-core: affected >= 1.143.12, < 1.169.39; fixed in 1.169.39
- npm @tanstack/vue-start: affected >= 1.143.12, < 1.168.56; fixed in 1.168.56
- npm @tanstack/solid-start: affected >= 1.143.12, < 1.168.57; fixed in 1.168.57
- npm @tanstack/react-start: affected >= 1.143.12, < 1.168.60; fixed in 1.168.60

## Suggested inspection (read-only)
- `npm ls @tanstack/start-server-core --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.
- `npm ls @tanstack/vue-start --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.
- `npm ls @tanstack/solid-start --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.
- `npm ls @tanstack/react-start --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on @tanstack/start-server-core, @tanstack/vue-start, @tanstack/solid-start, @tanstack/react-start.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-qx66-fv34-fjm8 (GitHub-reviewed advisory GHSA-qx66-fv34-fjm8 lists affected ranges: npm @tanstack/start-server-core >=1.143.12 =1.143.12 =1.143.12 =1.143.12 <1.168.56)
- Verified: https://osv.dev/vulnerability/GHSA-qx66-fv34-fjm8 (OSV record GHSA-qx66-fv34-fjm8 lists affected ranges: npm @tanstack/start-server-core >=1.143.12 =1.143.12 =1.143.12 =1.143.12 <1.168.56 (fixed))

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