CVE-2018-3711 in Fastify
Summary
by MITRE
Fastify node module before 0.38.0 is vulnerable to a denial-of-service attack by sending a request with "Content-Type: application/json" and a very large payload.
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Analysis
by VulDB Data Team • 03/21/2023
The vulnerability identified as CVE-2018-3711 affects the Fastify node module version 0.38.0 and earlier, presenting a significant denial-of-service risk that can be exploited through carefully crafted HTTP requests. This vulnerability stems from the module's inadequate handling of large JSON payloads when the Content-Type header is explicitly set to application/json, creating a scenario where malicious actors can consume excessive system resources and potentially disrupt service availability for legitimate users.
The technical flaw resides in Fastify's request parsing mechanism which fails to implement proper rate limiting or size constraints on incoming JSON data when the content type is specifically identified as application/json. When a request containing a large JSON payload is received, the module attempts to parse and process the entire payload without adequate safeguards, leading to memory exhaustion and potential process crashes. This behavior creates a resource exhaustion condition where the server's memory allocation is rapidly consumed, ultimately resulting in service unavailability.
The operational impact of this vulnerability extends beyond simple service disruption as it can be exploited in various attack scenarios including distributed denial-of-service attacks, resource exhaustion attacks, and potentially more sophisticated exploitation techniques that leverage the module's parsing behavior to cause cascading failures. The vulnerability affects any system running Fastify versions prior to 0.38.0 and can be particularly damaging in high-traffic environments where the module is responsible for handling numerous concurrent requests. Attackers can craft payloads that are several megabytes or even larger, consuming system resources at an exponential rate and potentially causing the entire application to become unresponsive.
The vulnerability aligns with CWE-400, which addresses "Uncontrolled Resource Consumption," and represents a classic example of how insufficient input validation and resource management can lead to denial-of-service conditions in web applications. From an ATT&CK perspective, this vulnerability maps to T1499.004, which covers "Endpoint Denial of Service," and demonstrates how improper handling of user-provided data can be leveraged to compromise system availability. The exploitation requires minimal technical skill and can be automated, making it particularly dangerous for production environments that lack proper input sanitization and rate-limiting measures.
Mitigation strategies should include immediate upgrading to Fastify version 0.38.0 or later, which implements proper payload size limits and resource management controls. Organizations should also implement application-level rate limiting, request size restrictions, and monitoring for unusual patterns of resource consumption. Additional defensive measures include configuring web application firewalls to detect and block suspicious request patterns, implementing proper logging and alerting mechanisms, and conducting regular security assessments of node.js applications to identify similar vulnerabilities in other modules or components. The fix implemented in version 0.38.0 demonstrates the importance of proper resource management in high-performance web frameworks and serves as a reminder of the critical need for input validation and resource constraints in modern application development practices.