CVE-2026-33807
CRITICAL
INFO
Priority: 0.04
BB Relevance:
78/100
Published: 2026-04-15
Modified: 2026-10-26
First seen: 2026-10-29
Status: active
Attack Surface
Network
Low Complexity
No Auth
No Interaction
Conf. Impact
Integ. Impact
CVSS Vector Breakdown
AV:
Network
AC:
Low
PR:
None
UI:
None
S:
Unchanged
C:
High
I:
High
A:
None
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.
Weakness Classification (1)
Affected Software (1)
| Vendor | Product | Version |
|---|---|---|
| fastify | fastify\/express | < 4.0.5 |
References & Advisories (2)
Vendor Advisory
Exploit
Mitigation
Vendor Advisory