CVE-2008-5529 in eTrust Antivirus
Summary
by MITRE
CA eTrust Antivirus 31.6.6086, 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 • 12/05/2017
The vulnerability described in CVE-2008-5529 represents a significant bypass mechanism within CA eTrust Antivirus version 31.6.6086 that specifically targets the interaction between antivirus software and web browsers. This flaw exploits the way antivirus systems analyze file content and file extensions during threat detection processes. The vulnerability manifests when Internet Explorer 6 or 7 is in use, creating a specific attack vector that leverages the browser's handling of HTML documents combined with the antivirus's file inspection methodology. The attack technique relies on manipulating the file's metadata and naming conventions to evade detection mechanisms that typically rely on both file extension analysis and content inspection.
The technical flaw stems from the antivirus software's insufficient validation of file headers and content patterns when processing HTML documents. By placing an MZ header at the beginning of an HTML document, attackers can exploit the software's reliance on file extensions as the primary indicator of file type. The MZ header is the standard signature for windows executable files, which typically triggers different inspection routines in antivirus software. When combined with filename modifications such as removing the extension entirely, or using .txt or .jpg extensions, the antivirus system becomes confused about the actual file type being processed. This technique specifically targets the heuristic analysis capabilities of the antivirus software, where the system attempts to identify malicious content based on both file characteristics and content patterns.
The operational impact of this vulnerability extends beyond simple detection bypass, as it demonstrates a fundamental weakness in the antivirus software's file classification and threat analysis processes. Attackers can leverage this vulnerability to deliver malicious payloads that would normally be detected by standard antivirus measures, effectively neutralizing the protection provided by the security software. The demonstration using CVE-2006-5745 exploit shows how this bypass technique can be applied to deliver known malware variants that have previously been successfully blocked by similar antivirus systems. This vulnerability essentially allows attackers to circumvent the layered defense mechanisms that antivirus software typically provides, potentially leading to system compromise and data breaches.
This vulnerability aligns with CWE-444, which describes "Inconsistent Interpretation of HTTP Requests ('HTTP Request Smuggling')" and CWE-20, "Improper Input Validation," as it demonstrates how inconsistent file handling and insufficient input validation can lead to security bypasses. The attack pattern follows techniques described in the ATT&CK framework under T1059.005, "Command and Scripting Interpreter: Visual Basic," and T1566, "Phishing," as it enables attackers to deliver malicious content through seemingly benign file types that bypass security controls. Organizations using CA eTrust Antivirus version 31.6.6086 are particularly vulnerable to this attack because the software's heuristics fail to properly correlate file headers with file extensions, creating a gap in threat detection that malicious actors can exploit.
The recommended mitigations include immediate software updates to newer versions of CA eTrust Antivirus that address this specific bypass mechanism, implementation of additional network-based security controls such as web application firewalls and content filtering systems, and enhanced user education regarding suspicious file attachments. Organizations should also consider implementing multiple layers of security controls beyond traditional antivirus software, including email filtering systems, network monitoring tools, and regular security assessments to identify similar vulnerabilities in their security infrastructure. The vulnerability underscores the importance of comprehensive security architectures that do not rely solely on signature-based detection methods and emphasizes the need for robust input validation and consistent file handling across all security tools in the ecosystem.