Cross-Site Scripting (XSS) in @tanstack/start-server-core (CVE-2026-102989)
Summary
Cross-site scripting in @tanstack/start-server-core (CVE-2026-102989). Confidential information can be exposed externally. Mitigation: upgrade to 1.169.39 or later.
Original description
The description as published by the source.
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…
Source: NIST National Vulnerability Database NVD GitHub Advisory
Auto-generated summary
Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.
A vulnerability tracked as CVE-2026-102989 has been found in @tanstack/start-server-core.
Confidential information can be exposed externally. CVSS score: 9.3/10.
What to do: upgrade @tanstack/start-server-core to 1.169.39 or later.
If unsure, ask your IT team or search "@tanstack/start-server-core CVE-2026-102989" on the vendor's site.
CVE-2026-102989 (@tanstack/start-server-core) — CWE-79 / CVSS v3 9.3
Attack vector: remote (network-reachable) / unauthenticated
Patched: 1.169.39 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.
Cross-site scripting (XSS) (CWE-79) exists in @tanstack/start-server-core.
Check the vendor advisory for the affected versions of @tanstack/start-server-core.
Severity: Critical (CVSS 9.3/10). Confidential information can be exposed externally.
Update to 1.169.39.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r '@tanstack/start-server-core' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.
Response actions
Concrete steps and command examples for SOC/SRE teams to execute in order
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1Identify exposure identify
grep -r '@tanstack/start-server-core' . | grep -v node_modulesリポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で
@tanstack/start-server-coreを grep し、稼働しているサービス・バージョンを把握する。 -
2Apply patch patch
Upgrade @tanstack/start-server-core to 1.169.39ステージング環境で 1.169.39 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。
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3Post-deployment verification verify
Confirm patched version is live in productionパッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。