CVE-2026-44574: Next.js has a Middleware / Proxy bypass through dynamic route parameter injection
Applications that rely on middleware to protect dynamic routes can be vulnerable to authorization bypass.
What it is
Applications that rely on middleware to protect dynamic routes can be vulnerable to authorization bypass. In affected deployments, specially crafted query parameters can alter the dynamic route value seen by the page while leaving the visible path unchanged, which can allow protected content to be rendered without passing the expected middleware check.
We now only honor internal route-parameter normalization in trusted routing flows and ignore externally supplied parameter encodings that should never have been accepted from ordinary requests.
If you cannot upgrade immediately, enforce authorization in route or page logic instead of relying solely on middleware path matching.
How to check
- Affected: next (npm) >= 15.4.0, < 15.5.16.
- Affected: next (npm) >= 16.0.0, < 16.2.5.
- Compare your installed version with the range above (command below).
How to fix
- Upgrade next to 15.5.16 or later.
- Upgrade next to 16.2.5 or later.
npm ls nextSources
- criticalCVE-2026-75604: Next.js: Unauthenticated Remote Code Execution on windows-hosted servers
- criticalCVE-2025-29927: Next.js middleware authorization bypass
- highSecrets leaked via NEXT_PUBLIC_ (or VITE_) environment variables
- highCVE-2026-44578: Next.js vulnerable to server-side request forgery in applications using WebSocket upgrades