CVE-2026-33807

Description

@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.

PUBLISHED Reserved 2026-03-23 | Published 2026-04-15 | Updated 2026-04-15 | Assigner openjs

Problem types

CWE-436: Interpretation Conflict

Product status

Credits

FredKSchott reporter

mcollina remediation developer

UlisesGascon remediation reviewer

climba03003 remediation reviewer

References

github.com/...xpress/security/advisories/GHSA-hrwm-hgmj-7p9c exploit

github.com/...xpress/security/advisories/GHSA-hrwm-hgmj-7p9c

cna.openjsf.org/security-advisories.html

cve.org (CVE-2026-33807)

nvd.nist.gov (CVE-2026-33807)

Download JSON