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HIGHCVE-2026-33804Published Modified CNA openjs

CVE-2026-33804: @fastify/middie vulnerable to middleware bypass via deprecated ignoreDuplicateSlashes option

@fastify/middie versions 9.3.1 and earlier are vulnerable to middleware bypass when the deprecated Fastify ignoreDuplicateSlashes option is enabled. The middleware path matching logic does not account for duplicate slash normalization performed by Fastify's router, allowing requests with duplicate slashes to bypass middleware authentication and authorization checks. This only affects applications using the deprecated ignoreDuplicateSlashes option. Upgrade to @fastify/middie 9.3.2 to fix this issue. There are no workarounds other than disabling the ignoreDuplicateSlashes option.

Metrics

CVSS v3.1
7.4
Severity
HIGH
Fixed in
9.3.2
Affected Products
1

Fix available

9.3.2
Affected packages
  • @fastify/middie / @fastify/middie
    < 9.3.2 (from 0)
    Fixed in 9.3.2
CVSS Vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
CVE-2026-33804: @fastify/middie vulnerable to middleware bypass via deprecated ignoreDuplicateSlashes option | HarborGuard CVE