CVE-2026-33804— @fastify/middie vulnerable to middleware bypass via deprecated ignoreDuplicateSlashes option
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，该漏洞源于当启用已弃用的ignoreDuplicateSlashes选项时，中间件路径匹配逻辑未考虑Fastify路由器的重复斜杠规范化，可能导致带有重复斜杠的请求绕过中间件身份验证和授权检查。
Possible ATT&CK Techniques 1 AI
T1190 · Exploit Public-Facing Application
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I. Basic Information for CVE-2026-33804
Vulnerability Information
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Vulnerability Title
@fastify/middie vulnerable to middleware bypass via deprecated ignoreDuplicateSlashes option
Source: CVE Program / CVE List V5
Vulnerability Description
@fastify/middie versions 9.3.1 and earlier are vulnerable to middleware bypass when the deprecated Fastify ignoreDuplicateSlashes option is enabled. The middleware path matching logic does not account for duplicate slash normalization performed by Fastify's router, allowing requests with duplicate slashes to bypass middleware authentication and authorization checks. This only affects applications using the deprecated ignoreDuplicateSlashes option. Upgrade to @fastify/middie 9.3.2 to fix this issue. There are no workarounds other than disabling the ignoreDuplicateSlashes option.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:H/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，该漏洞源于当启用已弃用的ignoreDuplicateSlashes选项时，中间件路径匹配逻辑未考虑Fastify路由器的重复斜杠规范化，可能导致带有重复斜杠的请求绕过中间件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)
Affected Products
| Vendor | Product | Affected Versions | CPE | Subscribe |
|---|---|---|---|---|
| @fastify/middie | @fastify/middie | 0 ~ 9.3.2 | - |
|
II. Public POCs for CVE-2026-33804
| # | POC Description | Source Link | Shenlong Link |
|---|
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IV. Related Vulnerabilities
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Same vendor: @fastify/middie
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@fastify/middie standalone engine vulnerable to Denial of Se -
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@fastify/middie vulnerable to authorization bypass via encod -
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V. Comments for CVE-2026-33804
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