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CVE-2025-31137

HighPublished

Remix and React Router allow URL manipulation via Host / X-Forwarded-Host headers

Published: Apr 1, 2025
Updated: Apr 2, 2025
Assigning CNA: GitHub_M
Evidence observed: Aug 4, 2026

Primary CVSS

7.5/ 10High

nvd · CVSS 3.0

CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS probability estimate

1.2%

Low · next 30 days

Percentile: 65.2%
Model date: Sep 21, 2026

EPSS is a statistical estimate, not a certainty or a measure of impact. Combine it with CVSS, KEV status, exposure and your environment.

Summary

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.

Sources

vulnerability-in-Remix-React-Router-CVE-2025-31137-PoC
CTF challenge replicating CVE-2025-31137 in Remix/React Router Express. Learn to exploit a server-side vulnerability to find the admin flag.

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