CVE-2026-33808
@fastify/express vulnerable to middleware authentication bypass via URL normalization gaps (duplicate slashes and semicolons)
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.
INFO
Published Date :
April 15, 2026, 9:29 a.m.
Last Modified :
April 15, 2026, 9:29 a.m.
Remotely Exploit :
Yes !
Source :
openjs
Affected Products
The following products are affected by CVE-2026-33808
vulnerability.
Even if cvefeed.io is aware of the exact versions of the
products
that
are
affected, the information is not represented in the table below.
No affected product recoded yet
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS 4.0 | CRITICAL | ce714d77-add3-4f53-aff5-83d477b104bb |
Solution
- Upgrade @fastify/express to v4.0.5 or later.
- Apply the latest security patches for the application.
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CVE-2026-33808 vulnerability anywhere in the article.