dbcve.org
Fastify\/middieApplication · Fastify

CVE-2026-14181

HIGH · 7.5 CVSS v3.1 Published 2026-07-01
Fix available
A fix is available. Upgrade to 9.3.3 or later.
See remediation →
84/100
Remediation priority · High
Remotely reachable No privileges Zero-click 8 weeks old

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
@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.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

@fastify/middie versions 9.1.0-9.3.2 have a denial-of-service vulnerability in the URL normalization step of the standalone engine. Malformed percent-encoded sequences (incomplete escapes or truncated multibyte sequences) cause the decoder to throw a synchronous exception that escapes the normalize step and terminates the Node.js process. Applications using the Fastify plugin path are unaffected because Fastify's error handler catches the exception.

MitigationUpgrade @fastify/middie to version 9.3.3 or migrate from the standalone engine API (middie.run) to the Fastify plugin path to ensure exceptions are caught by the framework error handler.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Fastify\/middieApplication
Affected:>= 9.1.0, < 9.3.3

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Check installed @fastify/middie version
    Run npm list @fastify/middie or check package.json dependencies to identify the exact version installed
    Affected if Version is 9.1.0 through 9.3.2 inclusive
  2. Identify if standalone engine API is in use
    Search codebase for calls to middie.run() or usage of the standalone middie engine exported via require('@fastify/middie')
    Affected if Code uses middie.run() or the standalone engine rather than registering @fastify/middie as a Fastify plugin
  3. Confirm Fastify plugin registration (unaffected path)
    Verify if middie is registered via fastify.register(require('@fastify/middie')) rather than calling middie.run() directly
    Affected if Middie is NOT registered as a Fastify plugin and standalone engine is used

A user is affected if @fastify/middie version is between 9.1.0 and 9.3.2 AND the application uses the standalone engine API (middie.run) instead of the Fastify plugin registration path.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 9.3.3 or later
Fixed in 9.3.3
Interim mitigation

Upgrade @fastify/middie to version 9.3.3 or migrate from the standalone engine API (middie.run) to the Fastify plugin path to ensure exceptions are caught by the framework error handler.

Recommended fix High confidence

@fastify/middie version 9.3.3

  1. Check the current version of @fastify/middie installed in your project (e.g., npm list @fastify/middie or view package.json)
  2. Update @fastify/middie to version 9.3.3 by running: npm install @fastify/[email protected] (or yarn add @fastify/[email protected] / pnpm add @fastify/[email protected])
  3. Verify the upgrade was successful by running npm list @fastify/middie
  4. Test your application, particularly any code paths that use middie.run with the standalone engine API, to confirm the vulnerability is mitigated
  5. Consider migrating from the standalone engine API to the Fastify plugin path as a defense-in-depth measure

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Fastify\/middie Scoped from the published advisory
  • Consultation2.0 h
  • Implementation2.0 h
  • Testing2.0 h
  • Review / QA1.0 h
7.0 hours of engineering $1,240
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-14181 in production — separate from our analysis above.

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What this is

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What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
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