CVE-2008-5538 in Prevx1
Summary
by MITRE
Prevx Prevx1 2, 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 identified as CVE-2008-5538 represents a significant security flaw in Prevx Prevx1 version 2, specifically affecting users operating Internet Explorer 6 or 7 browsers. This weakness stems from the software's inadequate file type detection mechanisms that fail to properly analyze executable content when presented with modified file naming conventions. The vulnerability operates through a sophisticated evasion technique that exploits the trust placed in file extensions by security scanning systems, creating a dangerous gap in malware detection capabilities.
The technical implementation of this vulnerability involves the manipulation of executable file headers within HTML documents to circumvent security checks. Attackers can place an MZ header - which is the standard marker for executable files in windows systems - at the beginning of malicious content while simultaneously altering the file extension to disguise the true nature of the payload. This technique can be applied to files with no extension, .txt extensions, or .jpg extensions, effectively bypassing the security controls that rely on traditional file extension analysis. The demonstration of this exploit using CVE-2006-5745 shows how this technique can be leveraged to deliver previously detected malware through seemingly benign file types.
The operational impact of this vulnerability extends beyond simple bypass of detection mechanisms, creating a serious threat vector that can compromise entire systems through social engineering and file execution bypass. When Internet Explorer 6 or 7 processes these modified documents, the browser's handling of the MZ header combined with the deceptive file naming creates an environment where malicious code can execute without triggering appropriate security warnings. This vulnerability specifically targets the intersection of browser security and file type validation, where the trust relationship between the security software and the browser's interpretation of file content becomes exploitable.
The security implications of CVE-2008-5538 align with common weakness enumerations such as CWE-156, which addresses the improper handling of input validation, and CWE-120, which deals with buffer overflow conditions. This vulnerability also maps to ATT&CK technique T1059, representing the execution of malicious code through legitimate system processes, and T1070, which involves the modification of file extensions to evade detection systems. The flaw demonstrates how attackers can exploit the inherent trust relationships between security tools, operating systems, and browsers to create persistent threats that remain undetected by traditional signature-based detection methods.
Mitigation strategies for this vulnerability require a multi-layered approach that addresses both the immediate detection bypass and the underlying architectural weaknesses. Organizations should implement enhanced file type validation that does not rely solely on extension matching, but instead performs content analysis to identify true file types regardless of their naming conventions. Security professionals must also consider updating or replacing Prevx Prevx1 version 2 with more robust security solutions that properly validate executable content, while ensuring that Internet Explorer 6 or 7 users are either upgraded to supported browser versions or protected through additional security measures. Network-based detection systems should be enhanced to identify suspicious patterns in file headers regardless of file extensions, and users should be educated about the risks of opening files with unconventional naming conventions.