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CVE-2026-33807

@fastify/express vulnerable to middleware path doubling causing authentication bypass in child plugin scopes

Published: Apr 15, 2026Updated: Jun 1, 2026 Sources: CVE List NVD BDUCWE-436
NVD MITRE
9.1CVSSCRITICAL
EPSS Score
0.4%
Top 65.8%
CISA KEV
Not in KEV
Exploits
No Known Exploits
Remediation
Patch Available

Description

@fastify/express v4.0.4 and earlier contains a path handling bug in the onRegister function that causes middleware paths to be doubled when inherited by child plugins. When a child plugin is registered with a prefix that matches a middleware path, the middleware path is prefixed a second time, causing it to never match incoming requests. This results in complete bypass of Express middleware security controls, including authentication, authorization, and rate limiting, for all routes defined within affected child plugin scopes. No special configuration or request crafting is required. Upgrade to @fastify/express v4.0.5 or later.

CVSS Vector Breakdown

AV:NAC:LPR:NUI:NS:UC:HI:HA:N
Exploitability
AV:NAttack Vector
Network
AC:LAttack Complexity
Low
PR:NPrivileges Required
None
UI:NUser Interaction
None
Scope
S:UScope
Unchanged
Impact
C:HConfidentiality
High
I:HIntegrity
High
A:NAvailability
None
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Weaknesses

CWE-436

Affected Products

@fastify/expressfastify
Library
OSS Libraries / web-framework
FastifyMatteo Collina
Library
OSS Libraries / web-framework
fastify\/expressfastify
Library
OSS Libraries / web-framework
fastifyoss-projectOSS Librariesaka fastify/middie, fastify-multipart
matteo collinaindividual-devOSS Libraries

Exploitability

Official Patch Available
Workaround Available

References

https://github.com/fastify/fastify-express/security/advisories/GHSA-hrwm-hgmj-7p9c
github.com
https://cna.openjsf.org/security-advisories.html
cna.openjsf.org
https://cna.openjsf.org/security-advisories.html
cna.openjsf.org

Timeline

Published
Apr 15, 2026
Last Updated
Jun 1, 2026

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