CVE-2008-5526 in Anti-virus
Summary
by MITRE
DrWeb Anti-virus 4.44.0.09170, 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 • 10/22/2018
The vulnerability described in CVE-2008-5526 represents a significant security flaw in DrWeb Anti-virus version 4.44.0.09170 that specifically affects users operating Internet Explorer 6 or 7 browsers. This weakness exploits the way antivirus software processes and identifies potentially malicious files, creating a pathway for attackers to circumvent security protections through simple file manipulation techniques. The vulnerability demonstrates how legacy browser compatibility requirements can introduce unexpected security gaps in security software implementations.
The technical mechanism behind this vulnerability involves the manipulation of file headers and extensions to deceive the antivirus detection system. When an attacker places an MZ header - which is the standard executable file signature used by windows operating systems - at the beginning of an HTML document, the antivirus software incorrectly interprets the file as an executable rather than a web document. This occurs because the software relies heavily on file signatures for initial detection, and the presence of the MZ header triggers a false positive that bypasses the normal HTML document analysis process. The attack can be executed by simply renaming the malicious file to have no extension, a .txt extension, or a .jpg extension, all of which are commonly accepted file types that would not raise immediate suspicion during web browsing.
The operational impact of this vulnerability is substantial as it allows attackers to deliver malware through seemingly benign web content that would normally be considered safe by typical browser security settings. When Internet Explorer 6 or 7 processes these manipulated files, the antivirus software fails to properly identify the malicious payload, effectively neutralizing its protective capabilities. This creates a dangerous scenario where users can inadvertently download and execute malware without any warning signs, as the system treats the file as a legitimate document. The vulnerability is particularly concerning because it leverages the widespread use of older Internet Explorer versions and the predictable behavior of antivirus software when encountering files with modified headers and extensions.
The security implications extend beyond simple malware delivery, as this vulnerability directly relates to the principle of defense in depth and the importance of proper file type validation. According to CWE standards, this represents a weakness in input validation and file processing, specifically categorized under CWE-20, which deals with improper input validation. The attack vector aligns with ATT&CK techniques for initial access and execution, particularly using the T1059.001 technique for command and script interpreter execution, where the malicious file is executed through browser-based attacks. Organizations using DrWeb Anti-virus in environments with older Internet Explorer installations face significant risk, as this vulnerability could be exploited in targeted attacks or mass distribution campaigns where the attackers leverage the predictable behavior of the antivirus software to bypass security controls.
Mitigation strategies should focus on immediate software updates and configuration changes to address this specific vulnerability. System administrators should ensure that all affected DrWeb Anti-virus installations are updated to versions that properly handle file headers and extensions regardless of browser compatibility requirements. Additionally, implementing network-level controls such as web application firewalls and content filtering systems can help detect and block suspicious file downloads even if the antivirus software fails to identify the threat. Organizations should also consider implementing strict file extension policies and disabling automatic execution of files with potentially dangerous combinations of headers and extensions. Regular security assessments should be conducted to identify similar vulnerabilities in other security software and ensure that all components of the security infrastructure properly validate file content rather than relying solely on header signatures or file extensions for threat detection.