CVE-2008-5520 in V3 Internet Security
Summary
by MITRE
AhnLab V3 2008.12.4.1 and possibly 2008.9.13.0, when Internet Explorer 6 or 7 is used, allows remote attackers to bypass detection of malware in an HTML document by placing an MZ header (aka "EXE info") at the beginning, and modifying the filename to have (1) no extension, (2) a .txt extension, or (3) a .jpg extension, as demonstrated by a document containing a CVE-2006-5745 exploit.
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Analysis
by VulDB Data Team • 12/03/2017
The vulnerability described in CVE-2008-5520 represents a significant bypass mechanism within AhnLab V3 Internet Security software versions 2008.12.4.1 and potentially 2008.9.13.0. This flaw specifically targets the software's malware detection capabilities when used in conjunction with Internet Explorer 6 or 7 browsers. The vulnerability operates through a sophisticated file extension manipulation technique that exploits the way security software processes and identifies potentially malicious content.
The technical implementation of this vulnerability relies on the strategic placement of an MZ header at the beginning of HTML documents, which is the characteristic signature of executable files in the windows operating system. This header, commonly known as "EXE info," serves as the initial indicator that identifies a file as an executable binary. By embedding this header at the start of an HTML document, attackers can effectively disguise malicious code within seemingly benign web content. The exploit demonstrates particular effectiveness when combined with filename modifications that remove traditional executable extensions or replace them with common file types such as .txt or .jpg extensions.
This vulnerability directly impacts the core functionality of anti-malware software by exploiting a fundamental weakness in file type detection and content analysis mechanisms. The bypass occurs because AhnLab V3's detection system fails to properly analyze the actual content of files when they are presented with misleading file extensions. The software's heuristic analysis and signature matching processes are circumvented through this technique, allowing malicious code to evade detection even when it contains known exploits such as CVE-2006-5745. This represents a critical failure in the software's ability to perform comprehensive content analysis beyond simple file extension matching.
The operational impact of this vulnerability extends beyond simple malware evasion to represent a broader threat to network security infrastructure. When attackers can bypass detection mechanisms in security software, they gain increased opportunities to deploy malicious payloads without triggering alerts or defensive measures. This vulnerability particularly affects organizations that rely on AhnLab V3 for protection, as it demonstrates how sophisticated attackers can manipulate security software behavior through file format manipulation. The implications are significant for enterprise security, as it suggests that even relatively robust anti-malware solutions can be defeated through creative exploitation of detection logic flaws.
Security professionals should recognize this vulnerability as a classic example of how file extension manipulation can bypass content-based security controls, aligning with common attack patterns documented in the attack framework. The technique utilized in this exploit demonstrates the importance of multi-layered detection approaches that do not rely solely on file extensions for threat identification. Organizations should implement additional verification measures beyond simple file type detection, including behavioral analysis and content inspection techniques that can identify malicious code regardless of file extension presentation.
The vulnerability also highlights the need for proper input validation and content analysis within security software, particularly when dealing with complex file formats that may contain embedded executable code. According to CWE standards, this represents a weakness in the software's ability to properly validate file content and structure, potentially classified under CWE-20 for improper input validation. Security teams should ensure that their anti-malware solutions perform comprehensive analysis of file content rather than relying on superficial indicators such as file extensions or simple header recognition.
Mitigation strategies should focus on updating to newer versions of AhnLab V3 that address this specific bypass mechanism, as well as implementing additional security controls that can detect malicious content regardless of file extension. Network administrators should consider deploying multiple layers of security, including web application firewalls, content filtering systems, and behavioral analysis tools that can identify suspicious patterns in web content. Regular security assessments should be conducted to verify that anti-malware solutions are properly configured to detect and prevent similar bypass techniques, ensuring that security controls remain effective against evolving attack methodologies.
The broader implications of this vulnerability underscore the importance of maintaining comprehensive security testing procedures that include testing for file extension manipulation and content obfuscation techniques. Security teams should regularly evaluate their detection capabilities against known bypass methods and ensure that their systems can properly identify malicious content regardless of how it is presented to the system. This vulnerability serves as a reminder that even sophisticated security solutions can be defeated through careful exploitation of detection logic flaws, emphasizing the need for continuous security improvement and vigilance against emerging threats.