Input validation error in Remix - CVE-2025-31137
Published: April 1, 2025 / Updated: June 19, 2026
Vulnerability identifier: #VU134932
CSH Severity: Medium
CVSS v4: 6.9 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N]
CVE-ID: CVE-2025-31137
CWE-ID: CWE-20
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows a remote attacker to spoof the URL used in an incoming request.
The vulnerability exists due to improper input validation in the Express adapter request handler when processing Host or X-Forwarded-Host headers. A remote attacker can send a specially crafted Host or X-Forwarded-Host header containing a URL pathname in the port section to spoof the URL used in an incoming request.
Affected software
Remix
React Router
React Router
How to mitigate CVE-2025-31137
Install security update from vendor's website.
Remix - update to 2.16.3
React Router - update to 7.4.1
React Router - update to 7.4.1