Authentication bypass via inherited path re-prefixing
Published Apr 16, 2026 · Updated Apr 16, 2026
Authentication bypass in Fastify @fastify/middie 9.3.1 and earlier allows remote attackers to reach protected child-plugin routes. The plugin re-prefixes inherited middleware paths when a child prefix overlaps a parent middleware path, so the resulting path silently fails to match requests. Applications are exposed when security middleware is registered in the parent scope and protected routes reside in affected child or nested scopes.
Summary
What happened
Authentication bypass in Fastify @fastify/middie 9.3.1 and earlier allows remote attackers to reach protected child-plugin routes. The plugin re-prefixes inherited middleware paths when a child prefix overlaps a parent middleware path, so the resulting path silently fails to match requests. Applications are exposed when security middleware is registered in the parent scope and protected routes reside in affected child or nested scopes.
The record
- CVE
- CVE-2026-6270
- Published
- Apr 16, 2026
- Updated
- Apr 16, 2026
- Vendor
- Fastify
- Product
- @fastify/middie
- Classifications
- CWE-436, T1190
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Apr 16, 2026CVE publishedPublication date reported by the CVE source.
- Apr 16, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
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- Affected versionversion=0 <9.3.2
What conditions does exploitation require?
What is affected?
Published CVSS scores
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Attacks
What attackers are doing with it
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Public exploit references
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Technologies
Your stack
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Your stack
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