@fastify/express vulnerable to middleware bypass via non-string mount paths in prefixed plugins

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-6556
StatePUBLISHED
Assigneropenjs
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-06-30 13:19:25 UTC
Updated2026-07-01 15:57:54 UTC
Description@fastify/express versions 4.0.6 and earlier only rewrite the plugin prefix for middleware mount paths when the path argument is a string. Non-string mount paths (arrays of paths and regular expressions) are left unprefixed inside prefixed plugin scopes, so middleware registered with those forms does not match the actual prefixed request path. Applications that use path-scoped middleware for authentication, authorization, rate limiting, or auditing on routes inside a prefixed scope can be bypassed by sending a request to the prefixed route, because Fastify still matches the route but the middleware is skipped. Patches: upgrade to @fastify/express 4.0.7. Workarounds: use string mount paths instead of arrays or regular expressions in prefixed plugins, or register one use call per path.

Risk And Classification

Primary CVSS: v3.1 9.1 CRITICAL from ce714d77-add3-4f53-aff5-83d477b104bb

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

EPSS: 0.002950000 probability, percentile 0.212940000 (date 2026-07-04)

Problem Types: CWE-285 | CWE-285 CWE-285: Improper Authorization

VersionSourceTypeScoreSeverityVector
3.1ce714d77-add3-4f53-aff5-83d477b104bbSecondary9.1CRITICALCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
3.1CNACVSS9.1CRITICALCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
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

NVD Known Affected Configurations (CPE 2.3)

TypeVendorProductVersionUpdateEditionLanguage
Application Fastify Fastify/express All All All All

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA @fastifyexpress @fastify/express affected 4.0.7 semver Not specified
CNA @fastifyexpress @fastify/express unaffected 4.0.7 semver Not specified

References

ReferenceSourceLinkTags
cna.openjsf.org/security-advisories.html ce714d77-add3-4f53-aff5-83d477b104bb cna.openjsf.org Vendor Advisory
github.com/fastify/fastify-express/security/advisories/GHSA-3wf5-7852-vcfq ce714d77-add3-4f53-aff5-83d477b104bb github.com Mitigation, Vendor Advisory
CVE Program record CVE.ORG www.cve.org canonical
NVD vulnerability detail NVD nvd.nist.gov canonical, analysis

Vendor Comments And Credit

Discovery Credit

CNA: Jvr2022 (en)

CNA: UlisesGascon (en)

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