CVE-2020-7699 in express-fileupload
Summary
by MITRE
This affects the package express-fileupload before 1.1.8. If the parseNested option is enabled, sending a corrupt HTTP request can lead to denial of service or arbitrary code execution.
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Analysis
by VulDB Data Team • 11/06/2020
The vulnerability identified as CVE-2020-7699 targets the express-fileupload npm package, specifically affecting versions prior to 1.1.8. This package serves as a middleware for handling file uploads in node.js applications and is widely used across the web development ecosystem. The flaw manifests when the parseNested option is enabled, which allows for parsing nested multipart form data structures. The vulnerability stems from inadequate input validation and error handling within the parsing logic, creating a dangerous condition where malformed HTTP requests can trigger unexpected behavior in the application. The affected package is commonly integrated into web applications that process file uploads, making it a critical security concern for organizations relying on node.js-based infrastructure.
The technical implementation of this vulnerability involves the improper handling of multipart form data parsing when nested structures are encountered. When parseNested is enabled, the package attempts to recursively process nested form fields, but fails to properly validate the structure of incoming data. This creates a path where maliciously crafted HTTP requests containing malformed multipart boundaries or corrupted data can cause the application to enter an infinite loop, consume excessive system resources, or execute arbitrary code. The vulnerability is classified under CWE-400 as a resource exhaustion issue and can also be categorized under CWE-94 when it leads to arbitrary code execution. The flaw operates at the application layer, specifically within the HTTP request processing pipeline where file upload handlers are invoked, making it particularly dangerous for web applications that accept user uploads.
The operational impact of CVE-2020-7699 extends beyond simple denial of service conditions to potentially enable complete system compromise. An attacker exploiting this vulnerability could cause sustained denial of service by consuming all available memory or CPU resources through crafted requests that trigger infinite loops in the parsing logic. When the vulnerability leads to arbitrary code execution, it provides attackers with a direct path to compromise the underlying application server, potentially allowing for data exfiltration, privilege escalation, or further network infiltration. The vulnerability affects web applications running on node.js platforms that utilize the express-fileupload middleware with nested parsing enabled, which represents a significant portion of modern web applications. Organizations using vulnerable versions face risks of service disruption, data loss, and potential unauthorized access to their infrastructure. The ATT&CK framework categorizes this vulnerability under T1499 for resource exhaustion attacks and T1059 for command and scripting interpreter usage when code execution occurs, making it a multi-faceted threat requiring comprehensive mitigation strategies.
Mitigation strategies for CVE-2020-7699 primarily involve immediate version updates to express-fileupload 1.1.8 or later, which contain the necessary patches to address the parsing logic flaws. Organizations should conduct thorough vulnerability assessments to identify all applications using the affected package and ensure proper patch management procedures are in place. Additionally, implementing request rate limiting and size constraints on file upload endpoints can provide defense-in-depth measures that reduce the impact of potential exploitation attempts. Network-level firewalls and web application firewalls should be configured to monitor for suspicious multipart form data patterns that could indicate exploitation attempts. The implementation of input validation and sanitization measures at multiple layers of the application architecture provides additional protection against malformed requests. Security teams should also consider disabling the parseNested option if nested form structures are not required, as this eliminates the vulnerable code path entirely. Regular security monitoring and automated vulnerability scanning should be implemented to detect similar issues in other dependencies and maintain ongoing security posture. Organizations should also review their application logs for signs of exploitation attempts and implement proper incident response procedures to address potential compromises.