CVE-2021-31933 in Chamilo
Summary
by MITRE • 05/01/2021
A remote code execution vulnerability exists in Chamilo through 1.11.14 due to improper input sanitization of a parameter used for file uploads, and improper file-extension filtering for certain filenames (e.g., .phar or .pht). A remote authenticated administrator is able to upload a file containing arbitrary PHP code into specific directories via main/inc/lib/fileUpload.lib.php directory traversal to achieve PHP code execution.
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Analysis
by VulDB Data Team • 12/07/2024
The vulnerability CVE-2021-31933 represents a critical remote code execution flaw in the Chamilo learning management system version 1.11.14 and earlier. This vulnerability stems from inadequate input validation and sanitization mechanisms within the file upload functionality, specifically within the main/inc/lib/fileUpload.lib.php component. The flaw allows authenticated administrators to bypass security restrictions and execute arbitrary PHP code on the target system. The vulnerability is particularly concerning because it leverages the privileged position of an administrator, enabling attackers to gain full control over the affected server. The issue manifests through improper handling of file extensions and directory traversal techniques that permit the upload of malicious files with extensions such as .phar or .pht, which can be executed as PHP code within the application context.
The technical exploitation of this vulnerability occurs through a combination of directory traversal and file extension filtering bypass mechanisms. Attackers can manipulate the file upload process to place malicious PHP code in specific directories where the application will execute the code as part of normal operations. The improper input sanitization allows attackers to craft file names that circumvent the expected validation checks, while the flawed file-extension filtering permits execution of files with potentially dangerous extensions. This vulnerability aligns with CWE-434, which describes insecure file upload vulnerabilities, and specifically relates to CWE-22, representing path traversal issues. The flaw demonstrates poor input validation practices where the application fails to properly validate user-supplied data before processing file uploads, creating an attack surface that enables arbitrary code execution.
The operational impact of CVE-2021-31933 extends beyond simple code execution, as it provides attackers with complete system compromise capabilities. Once an authenticated administrator account is compromised, attackers can execute arbitrary commands on the server, potentially leading to data exfiltration, system infiltration, or further lateral movement within the network. The vulnerability can be exploited to establish persistent backdoors, modify application behavior, or access sensitive user data stored within the Chamilo platform. This represents a significant risk to educational institutions relying on Chamilo for their learning management needs, as the compromise of a single administrative account can result in complete system takeover. The vulnerability's exploitation aligns with ATT&CK technique T1059.007, which covers scripting through PHP, and T1566, covering spearphishing with a payload, as attackers may need to first gain administrative access through social engineering or credential compromise before exploiting this specific vulnerability.
Organizations should immediately implement multiple layers of defense to mitigate this vulnerability. The primary mitigation involves applying the vendor-provided patches or updates that address the input sanitization and file extension validation issues within the fileUpload.lib.php component. Additionally, administrators should implement strict file upload restrictions, including whitelisting of allowed file extensions and implementing proper file name validation to prevent directory traversal attacks. Network segmentation and monitoring should be enhanced to detect unusual file upload activities or attempts to access restricted directories. The implementation of web application firewalls can help detect and block malicious file upload attempts, while regular security audits should verify that file upload functionality properly validates all user inputs. Organizations should also consider implementing principle of least privilege access controls, ensuring that administrative privileges are only granted to users who require them for legitimate operations. Regular security training for administrators can help prevent credential compromise that would be necessary to exploit this vulnerability, while automated vulnerability scanning should be employed to identify similar issues in other components of the system.