Vulnerability Description
The @fastify/express plugin adds full Express compatibility to Fastify. A security vulnerability exists in @fastify/express prior to version 4.0.3 where middleware registered with a specific path prefix can be bypassed using URL-encoded characters (e.g., `/%61dmin` instead of `/admin`). While the middleware engine fails to match the encoded path and skips execution, the underlying Fastify router correctly decodes the path and matches the route handler, allowing attackers to access protected endpoints without the middleware constraints. The vulnerability is caused by how @fastify/express matches requests against registered middleware paths. This vulnerability is similar to, but differs from, CVE-2026-22031 because this is a different npm module with its own code. Version 4.0.3 of @fastify/express contains a patch fort the issue.
CVSS Score
HIGH
Related Weaknesses (CWE)
References
- https://github.com/fastify/fastify-express/commit/dc02a3fe1387f945143f22597baa42
- https://github.com/fastify/fastify-express/security/advisories/GHSA-g6q3-96cp-5r
FAQ
What is CVE-2026-22037?
CVE-2026-22037 is a vulnerability with a CVSS score of 8.4 (HIGH). The @fastify/express plugin adds full Express compatibility to Fastify. A security vulnerability exists in @fastify/express prior to version 4.0.3 where middleware registered with a specific path pref...
How severe is CVE-2026-22037?
CVE-2026-22037 has been rated HIGH with a CVSS base score of 8.4/10. Review the CVSS metrics above for detailed severity breakdown.
Is there a patch for CVE-2026-22037?
Check the references section above for vendor advisories and patch information. Review vendor security bulletins for remediation guidance.