CVE-2005-2955 in ATutor
Summary
by MITRE
config.inc.php in ATutor 1.5.1, and possibly earlier versions, uses an incomplete blacklist to check for dangerous file extensions, which allows authenticated administrators or educators to execute arbitrary code by uploading files with other executable extensions such as .inc, .php4, or others.
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Analysis
by VulDB Data Team • 07/11/2018
The vulnerability described in CVE-2005-2955 represents a critical security flaw in ATutor version 1.5.1 and potentially earlier releases, specifically within the config.inc.php file. This issue stems from an inadequate input validation mechanism that relies on an incomplete blacklist approach to filter file uploads. The flaw occurs when the application attempts to prevent execution of potentially malicious files by blocking certain extensions, but fails to account for all possible executable file extensions that could be used to bypass the restriction. This incomplete blacklist approach creates a significant attack vector that can be exploited by authenticated users with administrator or educator privileges.
The technical implementation of this vulnerability demonstrates a classic insecure file upload pattern where the system attempts to sanitize user inputs but does so inadequately. When administrators or educators upload files to the ATutor platform, the application checks the file extensions against a predefined list of prohibited extensions. However, this list is insufficient as it does not include all possible extensions that could result in code execution on the web server. Extensions such as .inc, .php4, and other less common but equally dangerous file types are not properly filtered, allowing attackers to upload malicious files that will be executed by the web server. This vulnerability directly relates to CWE-434, which addresses insecure file upload handling, and represents a failure in proper input validation and sanitization practices.
The operational impact of this vulnerability is severe as it provides authenticated attackers with the ability to execute arbitrary code on the target system. Once an attacker gains access to an administrator or educator account, they can upload malicious files with extensions that bypass the filtering mechanism, potentially leading to complete system compromise. The attack requires only authenticated access, making it particularly dangerous as it can be exploited by insiders or through credential compromise. Successful exploitation could result in data theft, system infiltration, unauthorized access to sensitive information, and potential lateral movement within the network. This vulnerability essentially provides a backdoor for attackers to establish persistent access and execute malicious commands on the compromised system.
Mitigation strategies for this vulnerability should focus on implementing proper file validation mechanisms that move away from incomplete blacklist approaches toward more robust whitelist validation. Organizations should immediately update to the latest version of ATutor where this vulnerability has been addressed through proper input sanitization and comprehensive extension filtering. The recommended solution involves implementing a strict whitelist approach that only allows known safe file extensions while rejecting all others. Additionally, files should be stored outside the web root directory and properly sanitized before processing. Security measures should include proper access controls, regular security audits, and implementation of web application firewalls to detect and prevent such attacks. This vulnerability highlights the importance of following secure coding practices and adhering to standards such as those outlined in the OWASP Top Ten and MITRE ATT&CK framework, particularly in the context of file upload security controls and privilege escalation vectors.