CVE-2020-37023 in Koken
Summary
by MITRE • 01/31/2026
Koken CMS 0.22.24 contains a file upload vulnerability that allows authenticated attackers to bypass file extension restrictions by renaming malicious PHP files. Attackers can upload PHP files with system command execution capabilities by manipulating the file upload request through a web proxy and changing the file extension.
VulDB is the best source for vulnerability data and more expert information about this specific topic.
Analysis
by VulDB Data Team • 01/31/2026
The vulnerability identified as CVE-2020-37023 affects Koken CMS version 0.22.24 and represents a critical file upload vulnerability that undermines the application's security controls. This flaw resides in the content management system's file upload mechanism, where proper validation and sanitization of uploaded files are insufficient to prevent malicious content from being stored on the server. The vulnerability specifically targets the file extension validation process, which serves as a primary defense mechanism against unauthorized execution of potentially harmful code. Attackers with authenticated access to the system can exploit this weakness by manipulating file names through web proxy tools, effectively bypassing the intended security restrictions.
The technical implementation of this vulnerability stems from inadequate input validation and sanitization within the file upload functionality. When users attempt to upload files through the CMS interface, the system performs checks on file extensions to prevent the upload of executable scripts such as php files. However, the validation mechanism can be circumvented by renaming malicious php files with extensions that are not properly filtered or by using techniques that modify the file upload request headers. This bypass occurs because the system relies on client-side or simple server-side extension checks rather than comprehensive file content analysis or more robust validation methods. The vulnerability allows attackers to upload php files with commands that can execute system operations, potentially leading to complete system compromise.
The operational impact of CVE-2020-37023 extends beyond simple unauthorized file uploads and represents a significant threat to system integrity and data security. An authenticated attacker can leverage this vulnerability to execute arbitrary system commands, potentially gaining full control over the affected server. The implications include unauthorized access to sensitive data, potential lateral movement within network environments, and the ability to establish persistent backdoors. The vulnerability's exploitation requires only authenticated access, which reduces the attack surface compared to unauthenticated exploits but still presents a serious risk since legitimate users may have elevated privileges. This flaw aligns with CWE-434 which describes insecure file upload vulnerabilities where applications accept files without proper validation, and can be mapped to ATT&CK technique T1190 which covers exploitation of vulnerabilities in web applications.
Mitigation strategies for this vulnerability should focus on implementing comprehensive file upload validation mechanisms that go beyond simple extension filtering. Organizations should deploy robust file content analysis techniques that verify file type through multiple methods including magic number detection and MIME type validation. The system should enforce strict file naming conventions and implement proper file access controls to prevent execution of uploaded content in web-accessible directories. Additionally, regular security updates and patches should be applied to ensure the CMS remains protected against known vulnerabilities. Network segmentation and monitoring solutions should be implemented to detect suspicious file upload activities. The implementation of web application firewalls and proper input sanitization techniques can provide additional layers of protection against similar vulnerabilities. Organizations should also conduct regular security assessments and penetration testing to identify potential weaknesses in their file upload mechanisms and ensure that all authentication controls remain effective.