# CVE-2026-33804

> Vulnerability · severity: **HIGH** (CVSS 7.4).

## Description

@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.

## Key facts

- **CVE ID:** CVE-2026-33804
- **Published:** 2026-04-16
- **CVSS severity:** HIGH
- **CVSS base score:** 7.4
- **CWE codes:** CWE-436

## Affected products

- `fastify:fastify\/middie`

## Primary sources

- NIST NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-33804

## Citation

> AI Analytics. CVE-2026-33804. Retrieved 2026-07-12 from https://api.ai-analytics.org/cve/CVE-2026-33804. Derived from NIST NVD. Licensed CC0.

---

*[Dataset catalog](https://api.ai-analytics.org/datasets/) · [AI Analytics](https://api.ai-analytics.org/) · CC0 1.0*