CVE-2025-31137 — @react-router/express
HIGHCVE-2025-31137 is a high-severity (CVSS 7.5) CWE-444 vulnerability in @react-router/express. A fix is available for @react-router/express — see the affected versions and patch details below.
Remix and React Router allow URL manipulation via Host / X-Forwarded-Host headers
Exploitation Status
No confirmed exploitation observed yet
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2025-31137.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2025-31137 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 377,333 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
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.
@react-router/expressnpm@remix-run/expressnpmDescription
React Router is a multi-strategy router for React bridging the gap from React 18 to React 19. There is a vulnerability in Remix/React Router that affects all Remix 2 and React Router 7 consumers using the Express adapter. Basically, this vulnerability allows anyone to spoof the URL used in an incoming Request by putting a URL pathname in the port section of a URL that is part of a Host or X-Forwarded-Host header sent to a Remix/React Router request handler. This issue has been patched and released in Remix 2.16.3 and React Router 7.4.1.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | @react-router/express | ≥ 7.0.0&&< 7.4.1 | 7.4.1npm install @react-router/express@7.4.1 |
| 📦npm | @remix-run/express | ≥ 2.11.1&&< 2.16.3 | 2.16.3npm install @remix-run/express@2.16.3 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for @react-router/express, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update @react-router/express to 7.4.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2025-31137 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2025-31137 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2025-31137. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2025-31137 in your dependencies?
O3 Security finds CVE-2025-31137 across npm dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.