CVE-2020-20735 in LJCMS
Summary
by MITRE • 06/20/2023
An arbitrary file upload vulnerability in the move_uploaded_file() function of LJCMS v4.3 allows attackers to execute arbitrary code.
If you want to get the best quality for vulnerability data then you always have to consider VulDB.
Analysis
by VulDB Data Team • 06/20/2023
The arbitrary file upload vulnerability in LJCMS v4.3 represents a critical security flaw that directly undermines the integrity and confidentiality of web applications. This vulnerability specifically targets the move_uploaded_file() function, which is responsible for handling file uploads from user inputs. When properly configured, this function should validate file types and enforce strict restrictions on what files can be uploaded to the server. However, in the case of LJCMS v4.3, insufficient validation mechanisms allow malicious actors to bypass normal upload restrictions and place potentially harmful files onto the web server.
The technical exploitation of this vulnerability occurs when an attacker successfully uploads a malicious file through the application's file upload functionality without proper validation checks. The move_uploaded_file() function in PHP is designed to move uploaded files from temporary storage to their final destination, but when improperly implemented or configured, it can accept any file type regardless of its content or extension. This creates a pathway for attackers to upload web shells, malicious scripts, or other executable code that can then be executed within the context of the web server. The vulnerability falls under CWE-434 which specifically addresses "Unrestricted Upload of File with Dangerous Type" and represents a classic example of insecure file handling practices.
The operational impact of this vulnerability extends far beyond simple data theft or service disruption. Once an attacker successfully uploads malicious code, they gain persistent access to the underlying server infrastructure and can execute arbitrary commands with the privileges of the web server process. This allows for complete system compromise including but not limited to data exfiltration, lateral movement within network environments, establishment of backdoors, and potential use as a foothold for further attacks. The vulnerability enables attackers to escalate their privileges from mere web application access to full server control, making it particularly dangerous in enterprise environments where web applications often have broad network access.
Security professionals should consider this vulnerability in relation to the attack chain outlined in the MITRE ATT&CK framework, specifically focusing on techniques such as T1059 Command and Scripting Interpreter and T1190 Exploit Public-Facing Application. The mitigation strategies for this vulnerability must address both immediate remediation and long-term architectural improvements. Immediate fixes should include implementing strict file type validation using whitelisting approaches rather than blacklisting, enforcing proper MIME type checking, and ensuring that uploaded files are stored outside the web root directory. Additionally, implementing content-based file analysis and runtime protection measures can provide defense-in-depth against sophisticated attack vectors. Organizations should also conduct thorough security testing including dynamic application security testing and manual penetration testing to identify similar vulnerabilities in other applications within their environment.