CVE-2026-33808
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:
X
AT:
Present
VC:
High
VI:
High
VA:
None
Description
Impact@fastify/express v4.0.4 and earlier fails to normalize URLs before passing them to Express middleware when Fastify router normalization options are enabled. This allows complete bypass of path-scoped authentication middleware via duplicate slashes when ignoreDuplicateSlashes is enabled, or via semicolon delimiters when useSemicolonDelimiter is enabled. In both cases, Fastify router normalizes the URL and matches the route, but @fastify/express passes the original un-normalized URL to Express middleware, which fails to match and is skipped. An unauthenticated attacker can access protected routes by manipulating the URL path. PatchesUpgrade 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