GHSA-9m65-766c-r333 — @tanstack/start-server-co…
GHSA-9m65-766c-r333 is a remote code execution vulnerability in @tanstack/start-server-core. A fix is available for @tanstack/start-server-core — see the affected versions and patch details below.
TanStack Start - Server Core: Inbound server-function request deserialization could invoke a sibling client-referenced server function
Real-World Exposure
How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.
@tanstack/start-server-corenpmDescription
Summary
A type-confusion bug in seroval ≤ 1.5.2 (upstream advisory) allowed a crafted JSON body sent to one TanStack Start server function to trigger invocation of a different client-referenced server function as a side effect of deserializing the request payload.
This is not an authentication bypass and not remote code execution. The mechanism only invokes server functions that the same client could already reach directly via /_serverFn/<id>, and the target function's full middleware chain — including any user-supplied authentication, authorization, and inputValidator — runs as it would on a direct call.
Impact
To be exploitable in any meaningful sense, an application would need to expose a client-referenced server function that:
- Performs a privileged side effect, and
- Has no authentication/authorization middleware, and
- Has no input validation
A function meeting all three is already directly callable by any unauthenticated client at its own endpoint, so the practical impact on correctly-written applications is nil. The residual concerns are:
A request to function A could cause function B to also execute, which may surprise observability/audit logging that keys off the request URL.
Request-level middleware (as opposed to per-function middleware) does not re-run for the inner invocation. Server-only functions (isClientReferenced: false) cannot be reached through this mechanism.
Patches
Upgrade to @tanstack/start-server-core ≥ 1.167.30 (or the equivalent dated release of @tanstack/react-start / @tanstack/solid-start). The fix bumps seroval to ≥ 1.5.3 and adds defense-in-depth to the serialization adapter plugin shape so adapter payloads cannot be confused with internal seroval node types.
Workarounds
If you cannot upgrade immediately, ensure every createServerFn(...) exposed to the client has both an .inputValidator(...) and authentication/authorization middleware via .middleware([...]). This is recommended regardless of this advisory.
Credits
- Mufeed VH of Winfunc Research
- Upstream fix coordinated with Seroval maintainers https://github.com/lxsmnsyc/seroval
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | @tanstack/start-server-core | all versions | 1.167.30npm install @tanstack/start-server-core@1.167.30 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for @tanstack/start-server-core, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update @tanstack/start-server-core to 1.167.30 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-9m65-766c-r333 is resolved across your whole dependency graph.
Workarounds
Do not deserialise data from untrusted sources: where the format allows it, restrict deserialisation to an explicit allowlist of expected types, and prefer a data-only format (JSON, Protobuf) over one that can reconstruct arbitrary objects until you can upgrade.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like GHSA-9m65-766c-r333 can be triaged on real exposure rather than presence alone.
Tailored to GHSA-9m65-766c-r333. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-9m65-766c-r333 in your dependencies?
O3 Security finds GHSA-9m65-766c-r333 across npm dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.