CVE-2026-22031— Fastify Middie Middleware Path Bypass
Quick assessment
Affected
fastify middie
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.
@fastify/middie是Fastify开源的一个中间件引擎。 @fastify/middie 9.1.0之前版本存在安全漏洞，该漏洞源于路径前缀匹配不当，可能导致中间件绕过。
Possible ATT&CK Techniques 1 AI
T1190 · Exploit Public-Facing Application
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I. Basic Information for CVE-2026-22031
Vulnerability Information
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Vulnerability Title
Fastify Middie Middleware Path Bypass
Source: CVE Program / CVE List V5
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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:L
Source: CVE Program / CVE List V5
Vulnerability Type
URL编码处理不恰当(Hex编码)
Source: CVE Program / CVE List V5
Vulnerability Title
@fastify/middie 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
@fastify/middie是Fastify开源的一个中间件引擎。 @fastify/middie 9.1.0之前版本存在安全漏洞，该漏洞源于路径前缀匹配不当，可能导致中间件绕过。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)
Affected Products
II. Public POCs for CVE-2026-22031
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Vendor Advisories for CVE-2026-22031 (1)
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V. Comments for CVE-2026-22031
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