CVE-2026-33804@fastify/middie vulnerable to middleware bypass via deprecated ignoreDuplicateSlashes option
Updated under an hour ago ()
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No exploitation reported and no EPSS estimate yet.
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@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.
- CVSS
- 7.4 HIGH (v3.1, CNA)CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
- Weakness (CWE)
- CWE-436
- Known exploited
- Not in CISA's KEV catalog
- EPSS (exploitation in the next 30 days)
- Not loaded for this CVE
- Assigned by
- openjs
- NVD analysis
- Analyzed
- Record last updated
- Apr 16, 2026
- First seen by InfoSec Signals
- Oct 9, 2026
Affected products
@fastify/middie @fastify/middie fastify_middie:fastify_middie (from the name) | before 9.3.2; 9.3.2 not affected | CNA record |
fastify fastify/middie fastify:fastify/middie | before 9.3.2 | NVD |
References
- https://github.com/fastify/middie/security/advisories/GHSA-v9ww-2j6r-98q6mitigation, vendor-advisory
- https://cna.openjsf.org/security-advisories.htmlvendor-advisory
The CVE record on cve.org NVD's entry
The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.