Vulnerability Description
@fastify/middie is the plugin that adds middleware support on steroids to Fastify. A security vulnerability exists in @fastify/middie prior to version 9.1.0 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. Version 9.1.0 fixes the issue.
CVSS Score
HIGH
Affected Products
| Vendor | Product | Versions |
|---|---|---|
| Fastify | Fastify\/Middie | < 9.1.0 |
Related Weaknesses (CWE)
References
- https://github.com/fastify/middie/commit/d44cd56eb724490babf7b452fdbbdd37ea2effbPatch
- https://github.com/fastify/middie/pull/245Issue TrackingPatch
- https://github.com/fastify/middie/releases/tag/v9.1.0ProductRelease Notes
- https://github.com/fastify/middie/security/advisories/GHSA-cxrg-g7r8-w69pExploitVendor Advisory
FAQ
What is CVE-2026-22031?
CVE-2026-22031 is a vulnerability with a CVSS score of 8.4 (HIGH). @fastify/middie is the plugin that adds middleware support on steroids to Fastify. A security vulnerability exists in @fastify/middie prior to version 9.1.0 where middleware registered with a specific...
How severe is CVE-2026-22031?
CVE-2026-22031 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-2026-22031?
Check the references section above for vendor advisories and patch information. Affected products include: Fastify Fastify\/Middie.