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TI-2026-26180 Aliases CVE-2026-33808GHSA-6hw5-45gm-fj88

@fastify/express vulnerable to middleware authentication bypass via URL normalization…

Priority HIGH 80CWE-436Published · Updated

Key facts

Attack vector
Network
Privileges required
None
User interaction
None
Attack complexity
Low
Attack requirements
Present
Impact type
—
Confidentiality · integrity · availability
High · High · None
Fix status
Fixed

Attack profile from CVSS 4.0 · CNA. Fix status from CNA and GitHub.

Summary

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.

Why it matters now

Exploitation Proof of concept CISA SSVC · not in CISA KEV
EPSS 0.00483 41st percentileScored 2026-11-07
Public exploit Yes 1 exploit referenceTagged by NVD
Fix Fixed @fastify/express (fastify): 4.0.5@fastify/express (npm): 4.0.5

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
Poc
Automatable
Yes
Technical impact
Total

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

VendorProductAffected versionsFixed inStatusSource
fastify@fastify/expressbefore 4.0.54.0.5Patch availableCNA
—@fastify/express (npm)before 4.0.54.0.5Patch availableGHSA-6hw5-45gm-fj88
  • @fastify/express Vendorfastify Affected before 4.0.5 Fixed in 4.0.5 Patch available CNA
  • @fastify/express (npm) Vendor— Affected before 4.0.5 Fixed in 4.0.5 Patch available GHSA-6hw5-45gm-fj88

CPE configurations NVD · 1

CPEVersionsRoleVendor
cpe:2.3:a:fastify:fastify\/express:*:*:*:*:*:node.js:*:*before 4.0.5Vulnerablefastify
  • cpe:2.3:a:fastify:fastify\/express:*:*:*:*:*:node.js:*:* Versions before 4.0.5 Vulnerable ·fastify

Remediation

  • Fix · CNA @fastify/express (fastify) Fixed in 4.0.5
  • Fix · GHSA-6hw5-45gm-fj88 @fastify/express (npm) Fixed in 4.0.5 Advisory →

Fixed in the same release

Records fixed by the same vendor advisory or release, as the CNA lists them.

  • Release ·

    fastify @fastify/express 4.0.5

    2 records Highest priority Priority HIGH 2 HIGH

    Other records, highest priority first

    • TI-2026-26179 @fastify/express vulnerable to middleware path doubling causing authentication bypass in child plugin scopesPriority HIGH 80
    Show all 2 records →

Timeline

  1. 2026-10-02 Threatist record created from CVE-2026-33808
  2. 2026-10-03 Alias added: GHSA-6hw5-45gm-fj88

References

Exploit 1

Advisory 2

Other 1

  • TI-2026-26179 @fastify/express vulnerable to middleware path doubling causing authentication bypass in child plugin scopes CVSS 3.1CRITICAL 9.1
  • TI-2026-05746 @fastify/express vulnerable to middleware bypass via non-string mount paths in prefixed plugins CVSS 3.1CRITICAL 9.1

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences