CVE-2008-5535 in Antivirus
Summary
by MITRE
Norman Antivirus 5.80.02, 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 • 12/02/2017
This vulnerability exists in Norman Antivirus version 5.80.02 where the antivirus software fails to properly analyze HTML documents when processed through Internet Explorer 6 or 7 browsers. The flaw stems from the software's heuristic detection mechanisms that rely on file extension analysis and header inspection patterns. Attackers can exploit this weakness by crafting malicious HTML documents that begin with an MZ header, which is typically associated with executable files, while simultaneously manipulating the filename extension to bypass traditional signature-based detection methods. This technique leverages the fact that the antivirus software's detection algorithms may not properly correlate the presence of executable headers with the document's actual file type when processed through the specific browser environment.
The technical implementation of this bypass involves placing the MZ header at the beginning of an HTML document, which is the signature used by windows executable files, combined with strategic filename manipulation that removes or alters the extension to .txt or .jpg formats. This approach specifically targets the heuristic analysis capabilities of the antivirus software by creating a false positive scenario where the system's file type detection logic becomes confused between legitimate document formats and potentially malicious executable content. The vulnerability demonstrates a critical flaw in the software's file type recognition and content analysis methodology, particularly when dealing with documents that contain embedded executable code structures.
The operational impact of this vulnerability extends beyond simple malware detection bypass, as it represents a sophisticated attack vector that can be used to deliver exploits like CVE-2006-5745, which targets vulnerabilities in Microsoft Office applications. This allows attackers to execute malicious code that would otherwise be detected by standard antivirus measures, potentially leading to full system compromise through the exploitation of the embedded vulnerability. The attack requires the victim to view the malicious document through Internet Explorer 6 or 7, which creates a specific execution environment where the antivirus fails to properly analyze the document's content and structure.
From a cybersecurity perspective, this vulnerability aligns with CWE-20, which describes improper input validation, and represents a classic case of insufficient security analysis during file type detection processes. The attack pattern follows principles outlined in the ATT&CK framework under T1059 for command and scripting interpreter and T1070 for indicator removal, as the malicious code is designed to bypass security controls and maintain persistence. The vulnerability demonstrates the importance of multi-layered detection approaches that do not rely solely on file extension analysis, but instead implement comprehensive content inspection and behavioral analysis mechanisms. Organizations using this version of Norman Antivirus are particularly vulnerable when their users interact with web-based content through older browser versions, as the attack vector specifically targets this combination of software components.
The recommended mitigations include immediate software updates to newer versions of Norman Antivirus that address this detection gap, implementation of browser security policies that restrict the execution of potentially malicious content, and deployment of additional security layers such as web application firewalls and advanced endpoint protection solutions. Organizations should also implement user education programs to reduce the risk of unintentional execution of malicious documents and establish robust incident response procedures to quickly identify and contain potential exploitation attempts. The vulnerability underscores the necessity of maintaining up-to-date security software and the importance of comprehensive testing of security solutions across different execution environments and browser configurations.