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                            CERT-Renater

                Note d'Information No. 2026/VULN1045
_____________________________________________________________________

DATE                : 19/10/2026

HARDWARE PLATFORM(S): /

OPERATING SYSTEM(S): Systems running@tanstack/react-start (npm)
                         versions prior to 1.168.60,
                    @tanstack/solid-start (npm) versions prior
                                 to 1.168.57,
                    @tanstack/start-server-core (npm) versions prior
                                  to 1.169.39,
               @tanstack/vue-start (npm) versions prior to 1.168.56.

====================================================================
https://github.com/advisories/GHSA-qx66-fv34-fjm8
_____________________________________________________________________


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

Critical severity GitHub Reviewed 

Vulnerability details

Package
@tanstack/react-start (npm)

Affected versions
>= 1.143.12, < 1.168.60

Patched versions
1.168.60

@tanstack/solid-start (npm)
Affected versions
>= 1.143.12, < 1.168.57

Patched versions
1.168.57

@tanstack/start-server-core (npm)
Affected versions
>= 1.143.12, < 1.169.39

Patched versions
1.169.39

@tanstack/vue-start (npm)
Affected versions

>= 1.143.12, < 1.168.56

Patched versions
1.168.56


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.
References

    GHSA-qx66-fv34-fjm8
    https://nvd.nist.gov/vuln/detail/CVE-2026-102989
    TanStack/router#8573
    TanStack/router@d521abd
    https://github.com/TanStack/router/releases/tag/release-2026-09-30-1747


Severity
Critical
9.3/ 10

CVSS v3 base metrics
Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
Required
Scope
Changed
Confidentiality
High
Integrity
High
Availability
None
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:N

EPSS score
0.516%(43rd percentile)

Weaknesses
Weakness CWE-79

CVE ID
CVE-2026-102989

GHSA ID
GHSA-qx66-fv34-fjm8

Source code
TanStack/router


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