CVE-2025-31137: remix-run react-router HTTP Request/Response Smuggling

Vulnerability summary

CVE-2025-31137 is a high (CVSS 7.5) HTTP Request/Response Smuggling vulnerability in remix-run react-router. EPSS estimates a 1.17% chance of exploitation in the next 30 days, higher than 66.8% of scored vulnerabilities.

Timeline

1. 01-04-2025
   PublishedVulnerability first disclosed.
2. 02-04-2025
   Last modifiedVulnerability information updated.

Description

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.

• CWE-444Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')The product acts as an intermediary HTTP agent (such as a proxy or firewall) in the data flow between two entities such as a client and server, but it does not interpret malformed HTTP requests or responses in ways that are consistent with how the messages will be processed by those entities that are at the ultimate destination.