CVE-2026-22031
@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.
Scoring
- Severity
- HIGH
- CVSS base score
- 8.4
- CVSS vector
- CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:L
- EPSS probability
- 0.48%
- CWE
- CWE-177
- Published
- 2026-01-19
- Last modified
- 2026-03-12
Affected products
- fastify middie
Weakness type
Related vulnerabilities
- CVE-2026-76172 — fast-uri vulnerable to host confusion via percent-encoded scheme normalization
- CVE-2026-67448 — Mailpit: WebSocket origin check bypass via percent-encoded path (regression of CVE-2026-22689)
- CVE-2026-15371 — Velociraptor Stored XSS in URL column types
- CVE-2026-59083 — Apache Tomcat: Incorrect URL decoding in RewriteValve may allow security control bypass
- CVE-2026-41041 — Apache Gravitino: URL path injection via unencoded user-supplied identifiers in MCP REST client f-string URL construction, enabling path traversal to unintended API endpoints.
- CVE-2026-6414 — @fastify/static vulnerable to route guard bypass via encoded path separators
- CVE-2026-29045 — Hono: Arbitrary file access via serveStatic vulnerability
- CVE-2026-22037 — @fastify/express vulnerable to Improper Handling of URL Encoding (Hex Encoding)