CVE-2017-5215 in B2J Contact Extension
Summary
by MITRE
The Codextrous B2J Contact (aka b2j_contact) extension before 2.1.13 for Joomla! allows a rename attack that bypasses a "safe file extension" protection mechanism, leading to remote code execution.
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Analysis
by VulDB Data Team • 09/30/2020
The Codextrous B2J Contact extension for Joomla! versions prior to 2.1.13 contained a critical vulnerability that enabled attackers to bypass file extension validation mechanisms through a rename attack technique. This flaw resided in the extension's file upload handling process where the system failed to properly validate file extensions before allowing file operations to proceed. The vulnerability specifically targeted the safe file extension protection mechanism that was designed to prevent execution of malicious files by restricting uploads to predefined safe extensions such as jpg, png, gif, and other image formats.
The technical implementation of this vulnerability allowed attackers to exploit a race condition or improper validation sequence where files could be initially uploaded with restricted extensions and then renamed to bypass the validation checks. This rename attack technique effectively circumvented the intended security controls by leveraging the fact that the extension's validation occurred at different stages of the file processing pipeline. The flaw was classified under CWE-434 as a "Upload of File Without a Properly Verified Security Check" which represents a common pattern in web application vulnerabilities where input validation is insufficient or occurs at inappropriate points in the processing workflow.
The operational impact of this vulnerability was severe as it enabled remote code execution capabilities for attackers who could upload malicious files and subsequently execute them on the target server. This occurred because the rename attack allowed attackers to transform benign file extensions into executable formats that the web server would process. The vulnerability was particularly dangerous in the context of Joomla! installations where the B2J Contact extension was commonly used for contact forms and file uploads, making it an attractive target for exploitation. Attackers could leverage this vulnerability to gain unauthorized access to the server, potentially leading to complete system compromise, data exfiltration, or further network infiltration.
Mitigation strategies for this vulnerability required immediate patching of the B2J Contact extension to version 2.1.13 or later where the rename attack mechanism was properly addressed. Organizations should have implemented multiple layers of defense including strict file type validation at multiple points in the upload process, proper file extension checking before any file operations, and implementation of file content verification mechanisms. The vulnerability also highlighted the importance of proper input validation and the need for defense-in-depth approaches as outlined in the MITRE ATT&CK framework where this could be categorized under initial access and execution techniques. Additional security measures included restricting file upload capabilities to authenticated users only, implementing proper file naming conventions that prevent extension manipulation, and deploying web application firewalls to monitor and block suspicious upload activities. The incident demonstrated the critical importance of validating file operations at all stages of processing and implementing comprehensive security controls to prevent bypass attacks that exploit timing or validation sequence weaknesses in web applications.