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CVE-2026-21884 high CVSS 8.2

Cross-Site Scripting (XSS) in react-router (CVE-2026-21884)

Summary

Cross-site scripting in react-router (CVE-2026-21884). Confidential information can be exposed externally. Exploitable via getKey. Mitigation: upgrade to 7.12.0 or later.

Original description

The description as published by the source.

React Router is a router for React. In @remix-run/react version prior to 2.17.3. and react-router 7.0.0 through 7.11.0, a XSS vulnerability exists in in React Router's API in Framework Mode when using the getKey/storageKey props during Server-Side Rendering which could allow arbitrary JavaScript execution during SSR if untrusted content is used to generate the keys. There is no impact if server-side rendering in Framework Mode is disabled, or if Declarative Mode () or Data Mode (createBrowserRouter/) is being used. This issue has been patched in @remix-run/react version 2.17.3 and react-router version 7.12.0.

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-2026-21884 has been found in react-router.
Attackers can target a specific entry point like getKey over the network to misuse the product.
Confidential information can be exposed externally. CVSS score: 8.2/10.
What to do: upgrade react-router to 7.12.0 or later.
If unsure, ask your IT team or search "react-router CVE-2026-21884" on the vendor's site.

CVE-2026-21884 (react-router) — CWE-79 / CVSS v3 8.2
Attack vector: remote (network-reachable) / unauthenticated
Attack surface: getKey / storageKey / createBrowserRouter
Patched: 7.12.0 — 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.

❓ What is the problem

Cross-site scripting (XSS) (CWE-79) exists in react-router. Attackers reach the vulnerable code path via getKey without authentication.

📍 Affected scope

Check the vendor advisory for the affected versions of react-router. Attack surface: getKey / storageKey / createBrowserRouter.

🔥 Severity

Severity: High (CVSS 8.2/10). Confidential information can be exposed externally.

🔧 How to fix

Update to 7.12.0.

🛡️ Workaround

Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.

🔍 Detection

Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'react-router' . 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

  1. 1
    Identify exposure identify 
    grep -r 'react-router' . | 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 react-router を grep し、稼働しているサービス・バージョンを把握する。

  2. 2
    Apply patch patch 
    Upgrade react-router to 7.12.0

    ステージング環境で 7.12.0 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。

  3. 3
    Post-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。

Affected packages

npm react-router
[{"type":"SEMVER","events":[{"introduced":"7.0.0"},{"fixed":"7.12.0"}]}]
npm @remix-run/react
[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"2.17.3"}]}]

References

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