CWE-177
Improper Handling of URL Encoding (Hex Encoding)
VariantDraft
Description
The product does not properly handle when all or part of an input has been URL encoded.
Hierarchy (View 1000)
Parents
Children
none
Related attack patterns (CAPEC)
CAPEC-120 · CAPEC-468 · CAPEC-64 · CAPEC-72
CVEs mapped to this weakness (4)
| CVE | Sev | Risk | CVSS | EPSS | KEV | Published | Description |
|---|---|---|---|---|---|---|---|
| CVE-2026-22037 | Hig | 0.48 | 8.4 | 0.00 | Jan 19, 2026 | 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. | |
| CVE-2026-22031 | Hig | 0.48 | 8.4 | 0.00 | Jan 19, 2026 | @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. | |
| CVE-2026-6414 | Med | 0.38 | 5.9 | 0.00 | Apr 16, 2026 | @fastify/static versions 8.0.0 through 9.1.0 decode percent-encoded path separators (%2F) before filesystem resolution, while Fastify's router treats them as literal characters. This mismatch allows attackers to bypass route-based middleware or guards that protect files served by @fastify/static. For example, a route guard on a protected path can be circumvented by encoding the path separator in the URL. Upgrade to @fastify/static 9.1.1 to fix this issue. There are no workarounds. | |
| CVE-2024-23983 | Med | 0.38 | — | 0.00 | Nov 11, 2024 | Improper handling of canonical URL-encoding may lead to bypass not properly constrained by request rules. |