CVE-2021-43421 in elFinder
Summary
by MITRE • 04/07/2022
A File Upload vulnerability exists in Studio-42 elFinder 2.0.4 to 2.1.59 via connector.minimal.php, which allows a remote malicious user to upload arbitrary files and execute PHP code.
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Analysis
by VulDB Data Team • 04/09/2022
The vulnerability identified as CVE-2021-43421 represents a critical file upload flaw within the Studio-42 elFinder file manager component affecting versions 2.0.4 through 2.1.59. This vulnerability resides in the connector.minimal.php file which serves as the core interface for file operations within the elFinder system. The flaw stems from inadequate input validation and sanitization mechanisms that fail to properly restrict file types and content during upload operations. Attackers can exploit this weakness to bypass security controls and upload malicious files including php scripts that can execute arbitrary code on the target server.
The technical implementation of this vulnerability demonstrates a classic insecure file upload scenario where the system does not adequately verify file extensions, MIME types, or file content before storing uploaded files. The connector.minimal.php script lacks proper file type validation checks that would normally prevent execution of potentially dangerous file formats. This allows attackers to upload php files with extensions such as .php, .phtml, or even disguised extensions that bypass simple filtering mechanisms. The vulnerability operates at the application layer and requires no authentication to exploit, making it particularly dangerous as it can be leveraged by remote attackers without prior access credentials.
From an operational impact perspective, this vulnerability creates a severe attack surface that can lead to complete system compromise. Successful exploitation enables attackers to execute arbitrary PHP code on the target server, potentially allowing them to establish persistent backdoors, escalate privileges, exfiltrate sensitive data, or use the compromised system as a launch point for further attacks within the network. The vulnerability affects organizations using elFinder in web applications, content management systems, and file sharing platforms where the component is integrated. The widespread adoption of elFinder in various web applications means that many organizations may be unknowingly exposed to this risk, creating a significant attack vector for threat actors.
Security professionals should implement multiple layers of defense to mitigate this vulnerability. Immediate remediation requires updating elFinder to versions 2.1.60 or later where the file upload validation has been strengthened. Organizations should also implement additional controls such as restricting file upload directories, implementing strict file type whitelisting, and configuring web servers to prevent execution of uploaded files in web-accessible directories. The vulnerability aligns with CWE-434 which describes insecure file upload conditions, and maps to attack techniques in the MITRE ATT&CK framework under T1190 for exploit public-facing application and T1059 for command and scripting interpreter. Network segmentation and monitoring for unusual file upload activities can provide additional detection capabilities for potential exploitation attempts.