CVE-2021-23394 in elfinder
Summary
by MITRE • 06/13/2021
The package studio-42/elfinder before 2.1.58 are vulnerable to Remote Code Execution (RCE) via execution of PHP code in a .phar file. NOTE: This only applies if the server parses .phar files as PHP.
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Analysis
by VulDB Data Team • 06/18/2021
The vulnerability identified as CVE-2021-23394 affects the studio-42/elfinder package versions prior to 2.1.58, presenting a critical remote code execution risk that leverages PHP code execution within .phar files. This flaw represents a significant security weakness in web-based file management systems that could allow attackers to execute arbitrary code on affected servers. The vulnerability specifically targets the handling of file uploads and processing within the elFinder file manager component, where improper validation of uploaded files creates an attack vector for malicious code deployment.
The technical exploitation of this vulnerability occurs through the manipulation of .phar file uploads, which are PHP archive files that can contain executable PHP code. When a server is configured to parse .phar files as PHP, the malicious file can be executed without proper authorization, allowing attackers to gain full control over the affected system. This represents a classic file upload vulnerability that falls under CWE-434, which specifically addresses the insecure handling of file uploads where the system fails to properly validate or sanitize file content. The vulnerability is particularly dangerous because it exploits a fundamental server configuration issue where .phar files are treated as executable PHP code rather than binary archives.
The operational impact of this vulnerability extends beyond simple code execution, as it can lead to complete system compromise and data breaches. Attackers can leverage this vulnerability to establish persistent access, escalate privileges, and potentially move laterally within network environments. The attack surface is particularly concerning for web applications that rely on elFinder for file management operations, as the vulnerability can be exploited through standard web interfaces without requiring special privileges or complex attack chains. This makes it an attractive target for automated exploitation tools and increases the risk of widespread compromise across affected installations.
Mitigation strategies for CVE-2021-23394 primarily focus on updating to the patched version 2.1.58 or later, which addresses the improper file validation and handling mechanisms. Organizations should also implement strict file type validation and content inspection to prevent .phar files from being processed as PHP code. Server configuration changes are essential, including ensuring that .phar files are not executed as PHP code and that proper file extension filtering is implemented. The vulnerability can be mapped to ATT&CK technique T1059.007 for Unix shell and T1190 for Exploit Public-Facing Application, as it represents a classic web application exploitation vector. Additional protective measures include implementing web application firewalls, restricting upload capabilities to trusted users only, and conducting regular security assessments to identify and remediate similar vulnerabilities in the application stack.