Security Digest · Vulnerability record
CVE-2026-102989: TanStack Router: Unauthenticated reflected XSS in TanStack Start server-function responses
TanStack Router is a client-first, server-capable, fully type-safe router and full-stack framework for the web.
CVSS 9.3 Critical EPSS 0.5% · p43
Should you act?
Critical and remotely reachable
No known exploitation yet, but it is network-reachable without credentials. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.
- 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.
From the GitHub advisory
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
Weakness type: CWE-79.
Product: @tanstack/start-server-core (npm) · Assigned by: GitHub_M · Published: 2026-10-13
Affected and fixed versions
| Ecosystem | Package | Vulnerable | First fixed |
|---|---|---|---|
| npm | @tanstack/start-server-core | >= 1.143.12, < 1.169.39 | 1.169.39 |
| npm | @tanstack/react-start | >= 1.143.12, < 1.168.60 | 1.168.60 |
| npm | @tanstack/solid-start | >= 1.143.12, < 1.168.57 | 1.168.57 |
| npm | @tanstack/vue-start | >= 1.143.12, < 1.168.56 | 1.168.56 |
| Vendor | Product | Affected versions (per 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 scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| GitHub_M | 3.1 | 9.3 Critical | CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:N |
| GitHub | 3.1 | 9.3 | CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:N |
- Attack vector: network (remotely reachable)
- Attack complexity: low
- Privileges required: none (no login)
- User interaction: required (a user must click/open something)
- Scope: changed (can affect other components)
CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.
Exploitation and urgency
- 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.
Timeline
- — CVE record published by GitHub_M
- — CVE record last updated
- — GitHub-reviewed advisory GHSA-qx66-fv34-fjm8 published (critical)
Sources and references
Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.
Vulnerability records
- GitHub Advisory GHSA-qx66-fv34-fjm8 github.com
- CVE.org record CVE-2026-102989 cve.org
- NVD entry CVE-2026-102989 nvd.nist.gov
Other references from the CVE record and advisory
- github.com github.com
- github.com github.com
- github.com github.com
- github.com github.com