---
title: "CVE-2026-102989: TanStack Router: Unauthenticated reflected XSS in TanStack Start server-function responses"
url: https://erroneo.us/security/cve/CVE-2026-102989/
description: "CVE-2026-102989 (@tanstack/start-server-core (npm)): TanStack Router is a client-first, server-capable, fully type-safe router and full-stack framework for…"
type: vulnerability-record
section: "Security Digest"
date_published: 2026-10-13
date_modified: 2026-10-15
publisher: erroneo.us
author: erroneo.us Security Desk
cve: "CVE-2026-102989"
kev: false
cvss: 9.3
epss: 0.00516
license: All rights reserved. Quote with attribution and a link.
---

# CVE-2026-102989: TanStack Router: Unauthenticated reflected XSS in TanStack Start server-function responses

**Signal:** Critical and remotely reachable. No known exploitation yet, but it is network-reachable without credentials. (Computed from CISA KEV, EPSS and CVSS; not an editorial verdict.)

## Should you act?

- No confirmed exploitation. It is not in CISA’s KEV catalog and CISA’s SSVC assessment records no known exploitation. That can change quickly after a public write-up; re-check if you are affected.
- EPSS 0.5% , percentile 43: FIRST’s model estimates a 0.5% chance of exploitation activity in the next 30 days, higher than 43% of all scored CVEs (low). EPSS is a probability, not a verdict.
- Needs a user to click or open something. Phishing makes that realistic, but it is not wormable.
- Only applies if your dependency tree includes @tanstack/start-server-core (npm) >= 1.143.12, < 1.169.39, fixed in 1.169.39 ; @tanstack/react-start (npm) >= 1.143.12, < 1.168.60, fixed in 1.168.60 ; @tanstack/solid-start (npm) >= 1.143.12, < 1.168.57, fixed in 1.168.57 ; @tanstack/vue-start (npm) >= 1.143.12, < 1.168.56, fixed in 1.168.56 . Check your lockfile, including transitive dependencies.

## What it is

TanStack Router is a client-first, server-capable, fully type-safe router and full-stack framework for the web. From 1.143.12 until 1.169.39 for @tanstack/start-server-core, 1.168.60 for @tanstack/react-start, 1.168.57 for @tanstack/solid-start, and 1.168.56 for @tanstack/vue-start, an unauthenticated attacker can place non-public fields in a server-function request payload so that attacker-controlled middleware state reaches the error path and a response-shaped object is accepted as an HTTP response. A crafted server-function URL can therefore return attacker-controlled HTML from the application's origin; when a visitor opens the URL, the injected script can access same-origin data and issue requests with the visitor's authority. This issue is fixed in @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.

## Affected packages

- npm `@tanstack/start-server-core` >= 1.143.12, < 1.169.39 → fixed: 1.169.39
- npm `@tanstack/react-start` >= 1.143.12, < 1.168.60 → fixed: 1.168.60
- npm `@tanstack/solid-start` >= 1.143.12, < 1.168.57 → fixed: 1.168.57
- npm `@tanstack/vue-start` >= 1.143.12, < 1.168.56 → fixed: 1.168.56

## Affected products (CVE record)

- TanStack router: < release-2026-09-30-1747
- @tanstack react-start: >= 1.143.12, < 1.168.60
- @tanstack solid-start: >= 1.143.12, < 1.168.57
- @tanstack start-server-core: >= 1.143.12, < 1.169.39
- @tanstack vue-start: >= 1.143.12, < 1.168.56

## Severity

- GitHub_M CVSS 3.1: 9.3 `CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:N`
- GitHub CVSS 3.1: 9.3 `CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:N`

## Exploitation

- CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
- CISA SSVC assessment: exploitation none , automatable no , technical impact total .
- FIRST EPSS (model of 2026-10-21): 0.52% probability of exploitation activity in the next 30 days; percentile 43.

## Sources

- [GitHub Advisory GHSA-qx66-fv34-fjm8](https://github.com/advisories/GHSA-qx66-fv34-fjm8)
- [CVE.org record CVE-2026-102989](https://www.cve.org/CVERecord?id=CVE-2026-102989)
- [NVD entry CVE-2026-102989](https://nvd.nist.gov/vuln/detail/CVE-2026-102989)
- [github.com](https://github.com/TanStack/router/security/advisories/GHSA-qx66-fv34-fjm8)
- [github.com](https://github.com/TanStack/router/pull/8573)
- [github.com](https://github.com/TanStack/router/commit/d521abd71c69f1ff010bb3def4d417cb5fa058cb)
- [github.com](https://github.com/TanStack/router/releases/tag/release-2026-09-30-1747)

---
Source page: https://erroneo.us/security/cve/CVE-2026-102989/ · Security Digest: https://erroneo.us/security/ · More: https://erroneo.us/llms.txt