CVE-2008-5534 in NOD32 Antivirus
Summary
by MITRE
ESET NOD32 Antivirus 3662 and possibly 3440, 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 • 11/30/2017
The vulnerability described in CVE-2008-5534 represents a significant bypass mechanism within ESET NOD32 Antivirus version 3662 and potentially 3440 that specifically targets the interaction between the antivirus software and Microsoft Internet Explorer versions 6 and 7. This flaw exploits a fundamental weakness in how the antivirus system processes and analyzes file types during web browsing sessions, creating a pathway for malicious actors to evade detection. The vulnerability operates by leveraging the way browsers handle file extensions and the underlying file structure, particularly when analyzing HTML documents that contain embedded malware payloads. The attack vector is particularly concerning because it targets the user's browsing experience rather than requiring direct system compromise or administrative privileges.
The technical implementation of this vulnerability relies on the manipulation of file headers and naming conventions to trick the antivirus detection system. Specifically, attackers can place an MZ header - which is the standard executable file signature used by windows operating systems - at the beginning of an HTML document. This header is typically associated with executable files, but when combined with strategic filename modifications, it confuses the antivirus engine's heuristic analysis. The filename manipulation involves removing the extension entirely or appending .txt or .jpg extensions, which causes the antivirus system to incorrectly categorize the file as benign. This technique exploits the fact that many antivirus systems rely heavily on file extension analysis as an initial filtering mechanism before conducting deeper content inspection.
The operational impact of this vulnerability extends beyond simple malware delivery, as it demonstrates a sophisticated approach to evasion that can bypass multiple layers of security. When combined with known exploits such as CVE-2006-5745, which targets vulnerabilities in Internet Explorer's handling of certain HTML elements, this vulnerability creates a multi-stage attack vector. The attack scenario involves an attacker crafting an HTML document that appears legitimate to users while containing malicious code that is disguised through the MZ header manipulation. This technique aligns with the ATT&CK framework's concept of "Masquerading" under tactic TA0001, where adversaries attempt to evade detection by disguising malicious files as benign ones. The vulnerability also relates to CWE-471, which addresses the issue of incorrect behavior by the program when handling input that is intended to be interpreted as a specific type of data.
The implications of this vulnerability are particularly severe in enterprise environments where users may be browsing untrusted websites or receiving suspicious email attachments. The fact that this vulnerability affects Internet Explorer versions 6 and 7 makes it especially concerning, as these versions were widely deployed in corporate environments during the period when this vulnerability was active. Organizations relying on ESET NOD32 for endpoint protection would have been vulnerable to attacks that could bypass their primary defense mechanisms. The vulnerability essentially allows attackers to perform a form of file extension manipulation that tricks the antivirus system into treating malicious code as safe content, creating a false sense of security for users who might trust their antivirus protection. This type of evasion technique represents a classic example of how security systems can be undermined by understanding and exploiting the specific behaviors and assumptions made by security software during file analysis.
Mitigation strategies for this vulnerability would have required immediate patching of the ESET NOD32 software to address the flawed detection logic and potentially involved implementing additional network-level controls to monitor and block suspicious file transfers. Organizations would have needed to update their security policies to address the specific threat of file extension manipulation and ensure that their antivirus systems were properly configured to analyze file content regardless of extension. The vulnerability also highlighted the importance of maintaining current antivirus definitions and ensuring that security systems were capable of detecting file types based on their actual content rather than relying solely on extension-based heuristics. This particular vulnerability underscores the critical need for robust content inspection mechanisms that can identify malicious code regardless of how it is disguised through file naming conventions or header manipulation techniques.