CVE-2026-33808

CRITICAL EPSS 38.0%
Published Apr 15, 20262mo ago · Modified Jun 17, 20261w ago
9.1 CVSS 4.0
Critical
Find Similar
Published Apr 15, 2026 2mo ago
Last Modified Jun 17, 2026 1w ago

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.

CVSS Details

Base Score
9.1
Exploitability
—
Impact
—
Vector string
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Attack Vector Network
Attack Complexity Low
Privileges Required None
User Interaction None
Scope X

Threat Intelligence

EPSS Exploit Probability
38.0% percentile
Exploit & Patch Status
Public Exploit Known
No Patch Available

Weaknesses 1

CWE-436

Affected Products 1

VendorProductVersionRange
fastifyfastify\/express* <4.0.5

References 2

  • cna.openjsf.org https://cna.openjsf.org/security-advisories.html
    Vendor Advisory
  • github.com https://github.com/fastify/fastify-express/security/advisories/GHSA-6hw5-45gm-fj88
    ExploitMitigationVendor Advisory

Remediation

No remediation data recorded yet

Check vendor advisories and the NVD entry for patch availability.