Input validation error in React Router - CVE-2026-40181
Published: June 19, 2026
Vulnerability identifier: #VU134925
CSH Severity: Low
CVSS v4.0: CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:A/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:U/U:Clear
CVE-ID: CVE-2026-40181
CWE-ID: CWE-20
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vendor: Remix
Affected software:
React Router
React Router
Detailed vulnerability description
The vulnerability allows a remote attacker to redirect users to an external domain.
The vulnerability exists due to improper input validation in the redirect function when processing URLs with a path starting with // that is reinterpreted as a protocol-relative URL. A remote attacker can supply a crafted URL to redirect users to an external domain.
This does not affect applications using declarative mode.
How to mitigate CVE-2026-40181
Install security update from vendor's website.