CVE-2008-5543 in AntiVirus
Summary
by MITRE
Symantec AntiVirus (SAV) 10, 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.
Be aware that VulDB is the high quality source for vulnerability data.
Analysis
by VulDB Data Team • 10/22/2018
The vulnerability described in CVE-2008-5543 represents a significant bypass mechanism within Symantec AntiVirus version 10, specifically targeting the way the antivirus software handles file type detection when Internet Explorer 6 or 7 is in use. This flaw exploits the fundamental assumptions that antivirus systems make about file identification and execution behavior, creating a pathway for malicious actors to evade detection. The vulnerability operates at the intersection of web browser security and endpoint protection, demonstrating how client-side applications can be leveraged to circumvent server-side security controls. This type of attack falls under the category of file extension manipulation and header spoofing techniques that have been commonly exploited in malware delivery mechanisms since the early 2000s.
The technical implementation of this vulnerability relies on the manipulation of executable file headers combined with strategic filename modification to trick antivirus engines into incorrectly identifying malicious content. When an HTML document contains an MZ header at its beginning, this creates a false positive for executable file detection, while simultaneously altering the filename extension to either no extension, .txt, or .jpg to bypass traditional file type scanning mechanisms. The specific example of CVE-2006-5745 exploit demonstrates how this technique can be used to deliver previously detected vulnerabilities through seemingly benign file formats. The flaw essentially allows attackers to create documents that appear to be harmless text or image files while containing executable code that the antivirus engine fails to properly analyze due to its reliance on filename extensions rather than content analysis.
The operational impact of this vulnerability extends beyond simple detection bypass, creating a dangerous attack vector that can be exploited in phishing campaigns, drive-by download scenarios, and social engineering attacks. When combined with Internet Explorer 6 or 7, which were prevalent browsers at the time of the vulnerability's discovery, the attack surface expands significantly as these browsers had known security limitations that made them more susceptible to such exploitation techniques. The vulnerability essentially creates a false sense of security for users who might trust the file extension as an indicator of safety, while the underlying executable content remains undetected by the antivirus protection system. This type of attack pattern aligns with the common threat actor methodology of using file extension manipulation to evade signature-based detection systems, a technique that has been documented in various threat intelligence reports and security advisories.
The mitigation strategies for this vulnerability require a multi-layered approach that addresses both the immediate technical flaw and broader security practices. Organizations should implement content-based file analysis rather than relying solely on filename extensions, which aligns with the principle of defense in depth and the recommendations found in the OWASP Top Ten security framework. The solution involves updating antivirus engines to properly analyze file headers regardless of extension, implementing more robust file type detection algorithms, and ensuring that security systems do not make assumptions about file safety based on superficial attributes. Additionally, browser security updates and the implementation of stricter content filtering mechanisms would help prevent exploitation of this vulnerability, as it specifically targets the interaction between web browsers and endpoint protection systems. This vulnerability serves as a reminder of the importance of comprehensive security analysis that considers all aspects of file behavior rather than relying on single-point detection methods, a principle that is fundamental to the NIST cybersecurity framework and aligns with the ATT&CK framework's concept of execution techniques that bypass traditional security controls.
This vulnerability represents a classic case of how security systems can be defeated through the exploitation of logical assumptions rather than technical weaknesses, demonstrating the importance of comprehensive testing and the need for security controls to account for adversarial behavior patterns. The issue highlights the gap between traditional signature-based detection and modern threat evasion techniques, where attackers can manipulate the very mechanisms designed to protect systems. The vulnerability's classification under CWE-20, which deals with improper input validation, underscores the fundamental flaw in the antivirus engine's approach to file analysis. Organizations must recognize that security systems are only as strong as their weakest detection mechanism, and that bypass techniques like this one can render even sophisticated protection systems ineffective if they rely on predictable patterns of behavior that attackers can exploit.