CVE-2026-33807

@fastify/express v4.0.4 and earlier contains a path handling bug in the onRegister function that causes middleware paths to be doubled when inherited by child plugins. When a child plugin is registered with a prefix that matches a middleware path, the middleware path is prefixed a second time, causing it to never match incoming requests. This results in complete bypass of Express middleware security controls, including authentication, authorization, and rate limiting, for all routes defined within affected child plugin scopes. No special configuration or request crafting is required. Upgrade to @fastify/express v4.0.5 or later.

CVSS 3.1

9.1CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

EPSS

0.4% chance of exploitation in the next 30 days; higher than 37% of CVEs (scores of 2026-10-26)

CWE

CWE-436

Published

2026-04-15

Modified

2026-10-26

Record from

the NVD, synced 2026-10-26

Affected

• fastify:fastify\/express

Packages (OSV)

References

• https://cna.openjsf.org/security-advisories.html
• https://github.com/fastify/fastify-express/security/advisories/GHSA-hrwm-hgmj-7p9c
• https://github.com/fastify/fastify-express/security/advisories/GHSA-hrwm-hgmj-7p9c

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