Vulnerability Details CVE-2026-33808
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.
Exploit prediction scoring system (EPSS) score
EPSS Score 0.002
EPSS Ranking 37.0%
CVSS Severity
CVSS v3 Score 9.1
References
Products affected by CVE-2026-33808
-
cpe:2.3:a:fastify:fastify/express:0.1.0
-
cpe:2.3:a:fastify:fastify/express:0.2.0
-
cpe:2.3:a:fastify:fastify/express:0.3.0
-
cpe:2.3:a:fastify:fastify/express:0.3.1
-
cpe:2.3:a:fastify:fastify/express:0.3.2
-
cpe:2.3:a:fastify:fastify/express:0.3.3
-
cpe:2.3:a:fastify:fastify/express:1.0.0
-
cpe:2.3:a:fastify:fastify/express:1.1.0
-
cpe:2.3:a:fastify:fastify/express:2.0.0
-
cpe:2.3:a:fastify:fastify/express:2.0.1
-
cpe:2.3:a:fastify:fastify/express:2.0.2
-
cpe:2.3:a:fastify:fastify/express:2.1.0
-
cpe:2.3:a:fastify:fastify/express:2.2.0
-
cpe:2.3:a:fastify:fastify/express:2.3.0
-
cpe:2.3:a:fastify:fastify/express:3.0.0
-
cpe:2.3:a:fastify:fastify/express:4.0.0
-
cpe:2.3:a:fastify:fastify/express:4.0.1
-
cpe:2.3:a:fastify:fastify/express:4.0.2
-
cpe:2.3:a:fastify:fastify/express:4.0.3
-
cpe:2.3:a:fastify:fastify/express:4.0.4