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

published 2026-10-13 26 d ago modified 2026-10-16 23 d ago also GHSA-qx66-fv34-fjm8 , EUVD-2026-98849

cvss: 9.3; version 3.1, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 0.5%; EPSS 0.5% chance of exploitation in 30 days, percentile 45%
public exploits: 0; none known

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.

Patch / fix

fixed in 4 links 3

npm @tanstack/start-server-core 1.169.39
npm @tanstack/react-start 1.168.60
npm @tanstack/solid-start 1.168.57
npm @tanstack/vue-start 1.168.56

github.com/TanStack/router@d521abd commit
github.com/TanStack/router#8573 pull request
github.com/TanStack/router/releases/tag/release-2026-09-30-1747 release

CISA SSVC

Exploitation: none
Automatable: no
Technical impact: total
Assessed: 25 d ago (2026-10-14)

Exploit prediction

0.54% chance of exploitation in the next 30 days, higher than 45% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by	version	score	vector
CNA	3.1	9.3	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

Affected packages

ecosystem	package	affected	fixed in
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

Affected products

TanStack router
@tanstack react-start
@tanstack solid-start
@tanstack start-server-core
@tanstack vue-start

Classification

Weakness

CWE-79 Improper Neutralization of Input During Web Page Generation

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

Summary