Fastify
CVE-2023-51701
MEDIUM
Vulnerability Assessment
| Weakness |
CWE
OWASP Top 10:2025
A06:2025 - Insecure Design
ASVS 5.0
V4 - API and Web Service HTTP request consistency
|
| Impact | CVSS score of 5.3 (MEDIUM). Attack characteristics: network attack vector, low complexity, no privileges required, no user interaction not required. EPSS exploitation probability: 0.23%. |
| Exploit ScenarioDerived | A remote attacker could manipulate HTTP request interpretation between frontend and backend servers by sending crafted requests to the affected application. No authentication is required to exploit this vulnerability. |
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Alert meAnalysisAIv1 – Mar 28, 2026
fastify-reply-from is a Fastify plugin to forward the current HTTP request to another server. Rated medium severity (CVSS 5.3), this vulnerability is remotely exploitable, no authentication required, low attack complexity. This HTTP Request/Response Smuggling vulnerability could allow attackers to manipulate HTTP request interpretation between frontend and backend servers.
Earlier versions of this analysis (1)
fastify-reply-from is a Fastify plugin to forward the current HTTP request to another server. A reverse proxy server built with @fastify/reply-from could misinterpret the incoming body by passing an
RemediationAI
A vendor patch is available. Apply the latest security update as soon as possible. Enforce strict HTTP parsing, normalize requests at proxy layer, use HTTP/2 end-to-end, reject ambiguous headers.
Affected Packages
Source: OSV (Open Source Vulnerabilities)
Affects your stack
Affects 1 package in npm
Checking this CVE against your own stacks and servers is part of the Basic plan and up.
Technical ContextAI · show details
This vulnerability is classified as HTTP Request/Response Smuggling (CWE-444), which allows attackers to manipulate HTTP request interpretation between frontend and backend servers. fastify-reply-from is a Fastify plugin to forward the current HTTP request to another server. A reverse proxy server built with @fastify/reply-from could misinterpret the incoming body by passing an header ContentType: application/json ; charset=utf-8. This can lead to bypass of security checks. This vulnerability has been patched in '@fastify/reply-from` version 9.6.0. Affected products include: Fastify Reply-From. Version information: version 9.6.0..
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- Exploit and PoC references, threat intelligence from 22 sources
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Severity by source
AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
Primary rating from GitHub Advisory · only source for this CVE.
CVSS VectorGitHub Advisory
Lifecycle Timeline
2DescriptionGitHub Advisory
fastify-reply-from is a Fastify plugin to forward the current HTTP request to another server. A reverse proxy server built with @fastify/reply-from could misinterpret the incoming body by passing an header ContentType: application/json ; charset=utf-8. This can lead to bypass of security checks. This vulnerability has been patched in '@fastify/reply-from` version 9.6.0.
Executive ViewAI
Organizations using fastify-reply-from should be aware of moderate risk from CVE-2023-51701 rated CVSS 5.3. Exploitation could compromise the security of affected deployments. Organizations should apply vendor updates when available and monitor for exploitation.
Apply vendor patch. If patching is delayed: restrict network access and enable monitoring.
Threat Intelligence Overview
NVD
CVE.org
EPSS
GitHub
How this decision was reached
The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.
What every action level means
SSVC AssessmentENISA
Priority Score
Attack Technique
Authentication bypass attacks exploit flaws in the verification mechanisms that control access to systems and applications.
HTTP request smuggling exploits inconsistencies in how front-end and back-end servers parse HTTP message boundaries.
Affected Products (CPE)GitHub Advisory
All versions of @fastify/oauth2 used a statically generated state parameter at startup time and were used across all req
A redirect vulnerability in the `fastify-static` module version >= 4.2.4 and < 4.4.1 allows remote attackers to redirect
Fastify is a fast and low overhead web framework, for Node.js. Rated high severity (CVSS 7.5), this vulnerability is rem
Prototype pollution vulnerability in fastify-multipart < 1.0.5 allows an attacker to crash fastify applications parsing
Fastify node module before 0.38.0 is vulnerable to a denial-of-service attack by sending a request with "Content-Type: a
A denial of service vulnerability exists in Fastify v2.14.1 and v3.0.0-rc.4 that allows a malicious user to trigger reso
A redirect vulnerability in the fastify-static module version < 4.2.4 allows remote attackers to redirect users to arbit
Authorization bypass in the @fastify/express middleware-compatibility plugin (versions 4.0.6 and earlier) lets unauthent
Authentication bypass in @fastify/express v4.0.4 and earlier allows remote unauthenticated attackers to access protected
Middleware bypass in Fastify Express plugin (fastify/express) allows complete circumvention of authentication, authoriza
Fastify is a web framework with minimal overhead and plugin architecture. Rated high severity (CVSS 8.8), this vulnerabi
Authentication and authorization bypass in @fastify/middie (Node.js middleware library for Fastify) allows remote unauth
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