CVE•Published 2026-04-16•Modified 2026-05-14•0 articles on news•6 live references•NVD data

CVE-2026-33804Fastify · Fastify\/middie

Vulnerability data via NVD (ingested)

CVSS v3.1

7.4

HIGH

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N

EPSS percentile

Exploit Prediction Scoring System · top 85% of all CVEs

Weaknesses (CWE)

CWE-436Interpretation Conflict

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.

Timeline

Published 2026-04-16

Modified 2026-05-14

External references

NVD MITRE Exploit-DB GitHub PoC Sploitus VulnCheck

Search for exposed instances

Shodan + Censys queries derived from NVD's CPE data. The vuln tag catches assets Shodan has explicitly linked to this CVE; the product / banner fingerprints find exposed instances even when the vuln tag was never applied (which is common).

Shodan · vuln tag0 hosts

vuln:CVE-2026-33804

Hosts Shodan has explicitly fingerprinted as vulnerable.

Shodan · product

product:"Fastify Fastify\/middie"

All exposed Fastify Fastify\/middie instances — cross-reference with the CVE's affected-version range.

Shodan · banner/body mention

http.html:"Fastify\/middie"

HTTP body or banner mentions "Fastify\/middie" — catches deploys Shodan didn't identify as a product.

More intel sources (5)

Shodan report

vuln:CVE-2026-33804