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.
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.