Goal Reached Thanks to every supporter — we hit 100%!

Goal: 1000 CNY · Raised: 1359 CNY

100%
Buy Us a Coffee

CVE-2026-33807— @fastify/express vulnerable to middleware path doubling causing authentication bypass in child plugin scopes

Quick assessment

Affected
fastify @fastify/express
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/express是Fastify开源的一个兼容性插件。 @fastify/express 4.0.4及之前版本存在安全漏洞，该漏洞源于onRegister函数中的路径处理错误导致中间件路径在被子插件继承时被重复添加，可能导致完全绕过Express中间件安全控制。

CVSS 9.1 · Critical EPSS 0.53% · P43

Possible ATT&CK Techniques 1 AI

T1190 · Exploit Public-Facing Application
Get alerts for future matching vulnerabilities Log in to subscribe

I. Basic Information for CVE-2026-33807

Vulnerability Information
Have questions about the vulnerability? See if Shenlong's analysis helps!
View Shenlong Deep Dive ↗

Although we use advanced large model technology, its output may still contain inaccurate or outdated information.Shenlong tries to ensure data accuracy, but please verify and judge based on the actual situation.

Vulnerability Title
@fastify/express vulnerable to middleware path doubling causing authentication bypass in child plugin scopes
Source: CVE Program / CVE List V5
Vulnerability Description
@fastify/express v4.0.4 and earlier contains a path handling bug in the onRegister function that causes middleware paths to be doubled when inherited by child plugins. When a child plugin is registered with a prefix that matches a middleware path, the middleware path is prefixed a second time, causing it to never match incoming requests. This results in complete bypass of Express middleware security controls, including authentication, authorization, and rate limiting, for all routes defined within affected child plugin scopes. No special configuration or request crafting is required. Upgrade to @fastify/express v4.0.5 or later.
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/express 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
@fastify/express是Fastify开源的一个兼容性插件。 @fastify/express 4.0.4及之前版本存在安全漏洞，该漏洞源于onRegister函数中的路径处理错误导致中间件路径在被子插件继承时被重复添加，可能导致完全绕过Express中间件安全控制。
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)

Shenlong Deep Dive — AI Deep Analysis

10-question deep dive: root cause, exploitation, mitigation, urgency. Read summary free, full version requires login.

Read summary Full analysis (login)

Affected Products

Vendor Product Affected Versions CPE Subscribe
fastify @fastify/express 0 ~ 4.0.5 -

II. Public POCs for CVE-2026-33807

# POC Description Source Link Shenlong Link
AI-Generated POC Premium

No public POC found.

Login to generate AI POC

III. Intelligence Information for CVE-2026-33807

请登录查看更多情报信息。

Vendor Advisories for CVE-2026-33807 (1)

Same Patch Batch · fastify · 2026-04-15 · 3 CVEs total

CVE-2026-33806 7.5 HIGH fastify vulnerable to Body Schema Validation Bypass via Leading Space in Content-Type Head
CVE-2026-33808 @fastify/express vulnerable to middleware authentication bypass via URL normalization gaps

IV. Related Vulnerabilities

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

V. Comments for CVE-2026-33807

No comments yet

Leave a comment