dbcve.org
Fastify\/middieApplication · Fastify

CVE-2026-2880

CRITICAL · 9.1 CVSS v3.1 Published 2026-02-27
Fix available
A fix is available. Upgrade to 9.2.0 or later.
See remediation →
100/100
Remediation priority · Urgent
Remotely reachable No privileges Zero-click

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
A vulnerability in @fastify/middie versions < 9.2.0 can result in authentication/authorization bypass when using path-scoped middleware (for example, app.use('/secret', auth)). When Fastify router normalization options are enabled (such as ignoreDuplicateSlashes, useSemicolonDelimiter, and related trailing-slash behavior), crafted request paths may bypass middleware checks while still being routed to protected handlers.

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 · moderate confidence

The @fastify/middie middleware engine < 9.2.0 fails to properly apply path-scoped middleware when Fastify's router normalization options (ignoreDuplicateSlashes, useSemicolonDelimiter, or related trailing-slash options) are enabled, allowing attackers to bypass authentication/authorization middleware by crafting request paths that circumvent middleware checks but still route to protected handlers.

MitigationUpgrade @fastify/middie to version 9.2.0 or higher; verify all path-scoped middleware (app.use('/secret', auth)) correctly protects routes after upgrading, especially if using router normalization options.

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:< 9.2.0

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
High
Integrity
High
Availability
None

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

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 inspect package.json dependencies to find the installed version
    Affected if The version is lower than 9.2.0
  2. Identify if router normalization options are enabled
    Search Fastify server configuration for options: ignoreDuplicateSlashes, useSemicolonDelimiter, or trailing-slash related options (trailingSlash, strictTrailingSlash)
    Affected if Any of these normalization options are set to true or a non-default value in the Fastify instance creation
  3. Confirm path-scoped middleware usage
    Search codebase for middleware registered with a path prefix, such as app.use('/path', middleware) or fastify.use('/path', handler)
    Affected if Path-scoped middleware is used to protect routes (e.g., authentication middleware on specific paths)
  4. Review the full middleware chain
    Examine the order and configuration of middleware in your Fastify application, particularly any middleware that depends on path matching for access control
    Affected if Authentication or authorization middleware relies on path matching and is registered before upgrading to 9.2.0

You are affected if @fastify/middie version is below 9.2.0 AND router normalization options are enabled AND your application uses path-scoped middleware for access control.

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 9.2.0 or later
Fixed in 9.2.0
Interim mitigation

Upgrade @fastify/middie to version 9.2.0 or higher; verify all path-scoped middleware (app.use('/secret', auth)) correctly protects routes after upgrading, especially if using router normalization options.

Recommended fix High confidence

@fastify/[email protected]

  1. Check current @fastify/middie version in project dependencies (package.json or package-lock.json)
  2. Run npm update @fastify/middie or npm install @fastify/[email protected] to upgrade to the fixed version
  3. Verify the upgrade completed successfully by checking the installed version with npm list @fastify/middie
  4. Run application tests to ensure functionality remains intact after upgrade
  5. Deploy the updated application
Caveat Review Fastify router normalization behavior changes in release notes if using ignoreDuplicateSlashes, useSemicolonDelimiter, or trailing-slash options

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
  • Implementation1.0 h
  • Testing3.0 h
  • Review / QA2.0 h
8.0 hours of engineering $1,390
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $2,224.

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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-2026-2880 in production — separate from our analysis above.

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What this is

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What belongs here
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  • Version or environment caveats, and links to real fixes
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