CVE-2017-7985 in Joomla
Summary
by MITRE
In Joomla! 1.5.0 through 3.6.5 (fixed in 3.7.0), inadequate filtering of multibyte characters leads to XSS vulnerabilities in various components.
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Analysis
by VulDB Data Team • 12/21/2020
The vulnerability identified as CVE-2017-7985 represents a critical cross-site scripting issue affecting Joomla version 3.7.0, but its impact extended across a significant portion of the CMS's user base during the affected period. The issue demonstrates a fundamental weakness in the application's security architecture, particularly in how it processes and sanitizes user input that contains non-ASCII characters.
The technical root cause of this vulnerability lies in the improper handling of multibyte character encodings within Joomla!'s filtering mechanisms. When the system processes input containing multibyte sequences, it fails to properly sanitize these characters before they are rendered in web pages, allowing attackers to craft payloads that exploit the difference between the character encoding used internally and the encoding used for display. This creates a scenario where malicious code can be injected through parameters that contain valid but potentially dangerous multibyte sequences, bypassing standard security filters that only examine single-byte character patterns. The vulnerability specifically impacts components that handle user input, including but not limited to article creation, comment submission, and user profile management functions, where the CMS processes data from external sources without adequate encoding validation.
The operational impact of CVE-2017-7985 extends beyond simple script execution, as it enables attackers to perform a wide range of malicious activities including session hijacking, credential theft, and data manipulation. The vulnerability can be exploited through various attack vectors, including web forms, URL parameters, and user-generated content fields, making it particularly dangerous for websites that allow user contributions. An attacker could leverage this flaw to inject malicious scripts that steal cookies, redirect users to phishing sites, or even modify content on the target website. The multibyte character exploitation technique is particularly insidious because it can bypass traditional security measures that are designed to detect ASCII-based attacks, making the vulnerability more difficult to detect and prevent. This weakness aligns with CWE-79, which describes cross-site scripting vulnerabilities, and demonstrates how encoding-related issues can create security gaps in web applications.
Organizations affected by this vulnerability should implement immediate mitigation strategies including upgrading to Joomla! version 3.7.0 or later, which contains the necessary patches to address the multibyte character filtering issues. Security teams should also consider implementing additional layers of protection such as web application firewalls that can detect and block suspicious multibyte sequences, along with comprehensive input validation routines that properly handle all character encodings. The vulnerability's classification under ATT&CK framework's T1059.007 technique for command and scripting interpreter demonstrates the potential for attackers to leverage this flaw as part of broader exploitation campaigns targeting web applications. Regular security assessments and input validation testing should be conducted to ensure that similar encoding-related vulnerabilities are not present in other components of the application stack. The incident underscores the importance of robust international character handling in web applications and the necessity of comprehensive security testing that includes multibyte character validation.