CVE-2008-5546 in Vba32 Antivirus
Summary
by MITRE
VirusBlokAda VBA32 3.12.8.5, 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 • 11/26/2017
The vulnerability identified as CVE-2008-5546 represents a significant bypass flaw in the VirusBlokAda VBA32 3.12.8.5 antivirus solution that specifically affects users operating Internet Explorer 6 or 7. This security weakness demonstrates how heuristic and signature-based detection mechanisms can be circumvented through strategic file naming and header manipulation techniques. The flaw exploits the way antivirus software processes and analyzes file types, particularly when dealing with HTML documents that contain embedded malicious content. The vulnerability specifically targets the detection algorithms that rely on file extensions and header analysis, creating a pathway for attackers to deliver malicious payloads that would otherwise be identified and blocked by standard security measures.
The technical implementation of this vulnerability involves the strategic placement of an MZ header at the beginning of HTML documents, which is the characteristic signature of windows executable files. This header manipulation, combined with deliberate filename obfuscation using no extension, .txt, or .jpg extensions, allows the malware to evade detection by the antivirus software. The MZ header serves as a deceptive mechanism that tricks the detection system into misclassifying the file type, as the software may interpret the header as indicating a legitimate executable rather than a malicious document. This technique leverages the fact that many antivirus solutions perform content analysis based on file headers and extensions, creating a window of opportunity for attackers to exploit these detection gaps. The vulnerability is particularly concerning because it demonstrates how attackers can utilize legitimate file format characteristics to bypass security controls that are designed to identify executable content.
The operational impact of this vulnerability extends beyond simple detection bypass, as it creates a persistent threat vector that can be exploited in various attack scenarios. When combined with known exploits such as CVE-2006-5745, this vulnerability enables attackers to deliver sophisticated malware payloads that can compromise user systems through web-based attacks. The attack surface is particularly dangerous in enterprise environments where Internet Explorer 6 and 7 are still in use, as these older browsers often lack modern security features and are more susceptible to exploitation. This vulnerability can be weaponized in phishing campaigns, drive-by download attacks, and other web-based threat vectors where attackers seek to bypass security controls without triggering alerts. The implications are particularly severe because the attack relies on the user's browser behavior rather than requiring complex social engineering or direct system compromise.
The mitigation strategies for this vulnerability require a multi-layered approach that addresses both the immediate detection bypass and broader security posture issues. Organizations should implement comprehensive file type validation mechanisms that do not rely solely on filename extensions or simple header analysis. The solution involves deploying more sophisticated heuristic analysis that can identify suspicious patterns regardless of file naming conventions. Security administrators should also consider implementing strict content filtering policies that analyze the actual content of HTML documents rather than relying on superficial file attributes. This vulnerability highlights the importance of following security best practices outlined in standards such as the CWE (Common Weakness Enumeration) categories related to improper input validation and insufficient input sanitization. Additionally, the ATT&CK framework would categorize this as a technique involving 'Masquerading' and 'Obfuscated Files or Information' where adversaries manipulate file characteristics to avoid detection. The recommended remediation includes updating to newer antivirus versions that properly handle header-based detection, implementing network-based intrusion detection systems, and conducting regular security awareness training to address the broader threat landscape.