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CVE-2026-6270— @fastify/middie vulnerable to middleware authentication bypass in child plugin scopes

Quick assessment

Affected
@fastify/middie @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 9.3.1及之前版本存在安全漏洞，该漏洞源于未在子插件引擎实例上注册继承的中间件，可能导致绕过身份验证和授权检查。

CVSS 9.1 · Critical EPSS 0.61% · P47

Possible ATT&CK Techniques 1 AI

T1078 · Valid Accounts
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I. Basic Information for CVE-2026-6270

Vulnerability Information
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Vulnerability Title
@fastify/middie vulnerable to middleware authentication bypass in child plugin scopes
Source: CVE Program / CVE List V5
Vulnerability Description
@fastify/middie versions 9.3.1 and earlier do not register inherited middleware directly on child plugin engine instances. When a Fastify application registers authentication middleware in a parent scope and then registers child plugins with @fastify/middie, the child scope does not inherit the parent middleware. This allows unauthenticated requests to reach routes defined in child plugin scopes, bypassing authentication and authorization checks. Upgrade to @fastify/middie 9.3.2 to fix this issue. There are no workarounds.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
解释冲突
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 9.3.1及之前版本存在安全漏洞，该漏洞源于未在子插件引擎实例上注册继承的中间件，可能导致绕过身份验证和授权检查。
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)

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Affected Products

Vendor Product Affected Versions CPE Subscribe
@fastify/middie @fastify/middie 0 ~ 9.3.2 -

II. Public POCs for CVE-2026-6270

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III. Intelligence Information for CVE-2026-6270

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Vendor Advisories for CVE-2026-6270 (1)

IV. Related Vulnerabilities

Same product: @fastify/middie
Same vendor: @fastify/middie
Same weakness: CWE-436

V. Comments for CVE-2026-6270

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