CVE-2013-4568 in MediaWiki
Summary
by MITRE
Incomplete blacklist vulnerability in Sanitizer::checkCss in MediaWiki before 1.19.9, 1.20.x before 1.20.8, and 1.21.x before 1.21.3 allows remote attackers to conduct cross-site scripting (XSS) attacks via certain non-ASCII characters in CSS, as demonstrated using variations of "expression" containing (1) full width characters or (2) IPA extensions, which are converted and rendered by Internet Explorer.
Be aware that VulDB is the high quality source for vulnerability data.
Analysis
by VulDB Data Team • 01/11/2022
The vulnerability CVE-2013-4568 represents a critical insecure input validation flaw in MediaWiki's CSS sanitization mechanism that affects multiple versions prior to the specified patches. This issue resides within the Sanitizer::checkCss function which is responsible for filtering and validating CSS content to prevent malicious code injection. The vulnerability stems from an incomplete blacklist approach that fails to properly account for certain non-ASCII character representations that can bypass the security checks. According to CWE-601, this constitutes a URL redirection vulnerability through improper input validation, specifically manifesting as an insecure direct object reference in the context of CSS processing.
The technical exploitation of this vulnerability relies on the manipulation of CSS properties using non-ASCII character sequences that are functionally equivalent to malicious CSS expressions but are not properly detected by the sanitization routine. Attackers can leverage full width Unicode characters or IPA (International Phonetic Alphabet) extensions to construct CSS code that appears benign but when processed by Internet Explorer renders as executable JavaScript. This technique exploits the browser's rendering engine behavior where these character variations are converted and interpreted as standard ASCII characters, thereby bypassing the security controls. The vulnerability specifically targets Internet Explorer's CSS parsing and execution mechanisms, making it particularly dangerous in environments where IE is the primary browser.
The operational impact of this vulnerability extends beyond simple XSS attacks as it allows remote attackers to inject malicious code that can execute in the context of the victim's browser session. This creates potential for session hijacking, credential theft, and the execution of arbitrary commands on affected systems. The vulnerability affects not just individual user sessions but can compromise entire wiki installations, particularly those with user-generated content where CSS styling is permitted. Organizations using MediaWiki for collaborative environments, documentation systems, or content management platforms face significant risk exposure, especially when users can submit CSS code that gets rendered in the browser. The vulnerability's exploitation requires minimal technical skill and can be automated, making it particularly dangerous for widespread deployment.
Mitigation strategies for CVE-2013-4568 should focus on implementing comprehensive input validation and adopting more robust security controls than simple blacklist approaches. Organizations should immediately upgrade to patched versions of MediaWiki, specifically versions 1.19.9, 1.20.8, and 1.21.3, which contain the necessary fixes. Additionally, implementing a whitelist-based approach for CSS validation, as recommended by the ATT&CK framework for defensive techniques, would provide more effective protection against similar vulnerabilities. The fix typically involves strengthening the CSS sanitization routine to properly handle Unicode character variations and ensure that all forms of CSS expressions are detected and neutralized. Network-level protections such as web application firewalls and content security policies should also be implemented to provide additional layers of defense. According to industry best practices, this vulnerability highlights the importance of proper encoding handling and the need for comprehensive testing of international character sets in security validation routines, as outlined in OWASP top ten security risks and secure coding guidelines.