Node.js CVE-2026-22037
HIGH
GHSA-g6q3-96cp-5r5m
Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata – not a confirmed exploit chain
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AccessCraft request with URL-encoded path
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ExploitBypass middleware path matching
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ExecutionRoute handler processes decoded path
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ImpactAccess protected endpoint without middleware constraints
Vulnerability Assessment
| Weakness |
CWE
OWASP Top 10:2025
A05:2025 - Injection
ASVS 5.0
V1 - Encoding and Sanitization URL encoding handling
|
| Exploitation Conditions | Authenticated user (PR:L) sending requests to @fastify/express versions prior to 4.0.3 with middleware configured to protect specific path prefixes. Fastify must be configured with Express compatibility layer enabled. |
| Impact | CVSS 8.4 (HIGH). Attack vector: Network. Complexity: High. Privileges required: Low. User interaction: None. Exploitation requires authentication. |
| Exploit ScenarioDerived | An attacker (requires authentication) could exploit this vulnerability to compromise the affected system. |
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Alert meAnalysisAIv1 – Mar 12, 2026
The @fastify/express plugin prior to version 4.0.3 allows authenticated attackers to bypass path-based middleware restrictions by submitting URL-encoded characters in requests, such as using /%61dmin instead of /admin. While the middleware engine fails to match the encoded path, the underlying Fastify router correctly decodes it and routes the request to handlers, enabling unauthorized access to protected endpoints. This affects Node.js applications using vulnerable versions of the plugin.
Earlier versions of this analysis (1)
The @fastify/express plugin adds full Express compatibility to Fastify. A security vulnerability exists in @fastify/express prior to version 4.0.3 where middleware registered with a specific path prefix can be bypassed using URL-encoded characters (e.g., /%61dmin instead of /admin). [CVSS 8.4 HIGH]
RemediationAI
Monitor vendor advisories for a patch. Restrict network access to the affected service where possible.
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
Affects fastify/expre. The @fastify/express plugin adds full Express compatibility to Fastify. A security vulnerability exists in @fastify/express prior to version 4.0.3 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 endp
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Severity by source
AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:L
Primary rating from GitHub Advisory · only source for this CVE.
CVSS VectorGitHub Advisory
Lifecycle Timeline
2DescriptionGitHub Advisory
The @fastify/express plugin adds full Express compatibility to Fastify. A security vulnerability exists in @fastify/express prior to version 4.0.3 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. The vulnerability is caused by how @fastify/express matches requests against registered middleware paths. This vulnerability is similar to, but differs from, CVE-2026-22031 because this is a different npm module with its own code. Version 4.0.3 of @fastify/express contains a patch fort the issue.
Executive ViewAI
CVE-2026-22037 presents notable security risk rated CVSS 8.4. Successful exploitation could significantly impact the confidentiality, integrity, or availability of affected systems. Organizations should apply vendor updates when available and consider compensating controls in the interim.
Apply vendor patch. If immediate patching is not feasible: (1) Implement network-level access controls to limit exposure; (2) Enable enhanced monitoring and alerting; (3) Apply principle of least privilege.
Threat Intelligence Overview
NVD
CVE.org
EPSS
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
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