# CVE-2026-33808

## Summary

- **CVE ID:** CVE-2026-33808
- **Severity:** CRITICAL
- **CVSS Score:** 9.1 (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)
- **CWE:** CWE-436
- **Published:** Apr 15, 2026
- **Last Modified:** Apr 15, 2026

## 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.

## Affected Products

- fastify — @fastify/express (0)
- fastify — @fastify/express (4.0.5)

## References

- [CNA](https://github.com/fastify/fastify-express/security/advisories/GHSA-6hw5-45gm-fj88)
- [CNA](https://cna.openjsf.org/security-advisories.html)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.48%
- **EPSS Percentile:** 40.1

---
_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-10._