fastify middle up to 9.3.2 Standalone Engine API uncaught exception

Summaryinfo

A vulnerability has been found in fastify middle up to 9.3.2 and classified as problematic. This issue affects some unknown processing of the component Standalone Engine API. This manipulation causes uncaught exception. This vulnerability is handled as CVE-2026-14181. The attack can be initiated remotely. There is not any exploit available. The affected component should be upgraded.

Detailsinfo

A vulnerability has been found in fastify middle up to 9.3.2 and classified as problematic. Affected by this vulnerability is an unknown part of the component Standalone Engine API. The manipulation with an unknown input leads to a uncaught exception vulnerability. The CWE definition for the vulnerability is CWE-248. An exception is thrown from a function, but it is not caught. As an impact it is known to affect availability. The summary by CVE 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.

It is possible to read the advisory at github.com. This vulnerability is known as CVE-2026-14181 since 06/30/2026. The exploitation appears to be easy. The attack can be launched remotely. The exploitation doesn't need any form of authentication. The technical details are unknown and an exploit is not publicly available.

Upgrading to version 9.3.3 eliminates this vulnerability.

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Productinfo

Vendor

• fastify

Name

• middle

Version

• 9.3.0
• 9.3.1
• 9.3.2

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CPE 2.2info

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