CVE-2026-14181
HighCVSS 7.5Exploitation Probability (EPSS)
Low risk23th percentile - higher than 23% of all known CVEs
Summary
Vulnerability in @fastify/middie versions 9.1.0 through 9.3.2 causes Node.js process termination when processing malformed percent-encoded sequences in request paths. The issue only affects the standalone engine API (middie.run), not the Fastify plugin path.
Risk Assessment
An attacker can send a crafted request with malformed percent encoding, immediately crashing the Node.js process and causing denial of service (DoS) for all connected clients until the application is restarted.
Recommendation
Upgrade @fastify/middie to version 9.3.3 immediately. If upgrade is not possible, migrate from the standalone engine API to the Fastify plugin path, where the framework error handler catches the exception.
Other vulnerabilities in @fastify/middie
See all- CVE-2026-33804High
Versions @fastify/middie 9.3.1 and earlier are vulnerable to middleware bypass when the deprecated ignoreDuplicateSlashes option is enabled. The middleware path matching logic does not account for duplicate slash normalization, allowing requests with duplicate slashes to bypass authentication and authorization checks.
- CVE-2026-22031High
The @fastify/middie plugin prior to version 9.1.0 has a vulnerability that allows bypassing registered middleware using URL-encoded characters. Attackers can access protected endpoints without the constraints imposed by the middleware.
- CVE-2026-14198Critical
A vulnerability in @fastify/middie versions 9.1.0 through 9.3.2 causes a mismatch in handling encoded slashes (%2F) between the middleware and Fastify's router. An attacker can bypass middleware used for authentication, authorization, rate limiting, or auditing by sending a crafted request with an encoded slash in the parameter position.
- CVE-2026-6270Critical
Versions of @fastify/middie up to 9.3.1 do not register inherited middleware directly on child plugin engine instances. This allows unauthenticated requests to bypass authentication and authorization checks for routes defined in child plugins.
- CVE-2026-2880Critical
A vulnerability in @fastify/middie versions < 9.2.0 can result in authentication/authorization bypass when using path-scoped middleware. When Fastify router normalization options are enabled, crafted request paths may bypass middleware checks.
Original NVD description (English source)
@fastify/middie versions 9.1.0 through 9.3.2 fail to guard the URL normalization step used by the standalone engine when incoming request paths contain malformed percent-encoded sequences. Inputs such as an incomplete percent escape or a truncated multibyte sequence cause the underlying decoder to throw synchronously, and the exception escapes the middie normalize step and terminates the Node.js process. The bypass affects applications that call middie.run directly on the standalone engine API, causing an immediate denial of service for all connected clients until restart. Applications using the Fastify plugin path are not affected because Fastifys error handler catches the exception. Patches: upgrade to @fastify/middie 9.3.3. Workarounds: migrate from the standalone engine API to the Fastify plugin path, where the framework error handler catches the exception.