@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.
Upgrade to @fastify/express v4.0.5 or later.
Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).
| Vendor | Product | Default status | Versions | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| fastify | @fastify/express | unaffected |
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History
Wed, 15 Apr 2026 10:00:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| 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. | |
| Title | @fastify/express vulnerable to middleware path doubling causing authentication bypass in child plugin scopes | |
| Weaknesses | CWE-436 | |
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| Metrics |
cvssV3_1
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MITRE
Status: PUBLISHED
Assigner: openjs
Published:
Updated: 2026-04-15T09:55:50.627Z
Reserved: 2026-03-23T19:48:48.715Z
Link: CVE-2026-33807
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