CVE-2026-14181CWE-248

@fastify/middie standalone engine vulnerable to Denial of Service via malformed percent-encoded paths

High · published July 1, 2026

CVSS v3.1
7.5
EPSS
1%
Percentile
41.9
In the wild
Unconfirmed
What it is

@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.

The record
Technical detail
CVSS v3.1
7.5 · HIGH
Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
CVSS v4.0
Not supplied
EPSS
0.00500 · 41.9th percentile
Weakness
CWE-248 · Uncaught Exception
Published
2026-07-01T11:42Z
EPSS history
Timeline
  • 01 JUL 11:42Z
    @fastify/middie standalone engine vulnerable to Denial of Service via malformed percent-encoded paths
    cvelistv5