CVE-2017-7989 in Joomla
Summary
by MITRE
In Joomla! 3.2.0 through 3.6.5 (fixed in 3.7.0), inadequate MIME type checks allowed low-privilege users to upload swf files even if they were explicitly forbidden.
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Analysis
by VulDB Data Team • 05/31/2020
The vulnerability identified as CVE-2017-7989 affects Joomla! content management systems version 3.2.0 through 3.6.5, representing a critical security flaw in the platform's file upload validation mechanisms. This issue stems from insufficient MIME type verification during file uploads, which creates a pathway for malicious actors to bypass intended security restrictions. The vulnerability specifically impacts the media manager component where users can upload various file types, and it allows unauthorized file execution through the exploitation of overly permissive file type validation logic. The flaw exists in the core file upload handling functionality that should have prevented certain file types from being uploaded based on predefined security policies.
The technical implementation of this vulnerability lies in the inadequate MIME type checking mechanism within Joomla!'s file upload validation system. When users attempt to upload files through the media manager, the system performs MIME type verification but fails to properly validate or enforce restrictions on specific file types such as swf files. This occurs because the validation process relies on potentially unreliable MIME type detection methods that can be easily manipulated or bypassed. The vulnerability essentially allows a low-privilege user account to upload a Shockwave Flash file despite explicit security policies that prohibit such file types, creating a potential vector for code execution and cross-site scripting attacks.
The operational impact of CVE-2017-7989 extends beyond simple file upload bypass, as it represents a fundamental weakness in the platform's access control and file validation mechanisms. Attackers can exploit this vulnerability to upload malicious swf files that may contain embedded javascript or other malicious code, potentially leading to session hijacking, data exfiltration, or full system compromise. The vulnerability particularly affects organizations using older Joomla's built-in file management capabilities while maintaining security policies around file type restrictions.
The security implications of this vulnerability align with CWE-434, which describes "Unrestricted Upload of File with Dangerous Type," a well-documented weakness in web application security that directly relates to the improper file type validation mechanisms. From an attacker's perspective, this vulnerability maps to multiple ATT&CK techniques including T1059.007 for script execution and T1566 for malicious file delivery. Organizations using affected Joomla! versions should immediately implement mitigations including upgrading to version 3.7.0 or later, which contains the necessary fixes to properly validate MIME types during file uploads. Additionally, administrators should review and tighten their file upload policies, implement additional validation layers, and consider implementing web application firewalls to monitor and block suspicious file upload attempts that may exploit this vulnerability. The fix implemented in version 3.7.0 addresses the root cause by strengthening the MIME type checking process and ensuring that file upload restrictions are properly enforced regardless of user privileges or access levels.