CVE-2005-3370 in ArcaVir 2005
Summary
by MITRE
Multiple interpretation error in ArcaVir 2005 package 2005-06-21 allows remote attackers to bypass virus scanning via a file such as BAT, HTML, and EML with an "MZ" magic byte sequence which is normally associated with EXE, which causes the file to be treated as a safe type that could still be executed as a dangerous file type by applications on the end system, as demonstrated by a "triple headed" program that contains EXE, EML, and HTML content, aka the "magic byte bug."
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Analysis
by VulDB Data Team • 07/28/2017
The CVE-2005-3370 vulnerability represents a critical file type interpretation flaw in the ArcaVir 2005 antivirus software package released on June 21, 2005. This vulnerability stems from a fundamental misclassification error in the antivirus engine's file type detection mechanism, where the software incorrectly interprets certain file formats based on their initial byte sequences. The core issue manifests when files containing the "MZ" magic byte sequence are processed by the antivirus scanner, as this sequence is traditionally associated with executable files in the Portable Executable format. However, the vulnerability allows attackers to craft malicious files that contain this signature in unexpected contexts, such as batch files with .BAT extensions, HTML documents with .HTML extensions, or email messages with .EML extensions, thereby bypassing the antivirus's normal scanning procedures.
The technical exploitation of this vulnerability occurs through a sophisticated manipulation of file headers and content structures that exploit the antivirus software's reliance on magic byte sequences for file type identification. When the ArcaVir scanner encounters a file with an "MZ" signature, it incorrectly categorizes the file as a safe executable type rather than recognizing it as a potentially malicious container file. This misclassification allows the malicious file to pass through the antivirus screening process undetected, while the embedded executable content remains fully functional and executable on the target system. The vulnerability is particularly dangerous because it enables the creation of "triple headed" programs that combine multiple file types within a single container, where the embedded EXE code can execute with elevated privileges and bypass standard security controls.
The operational impact of this vulnerability extends beyond simple bypass of antivirus protection, as it fundamentally undermines the trust model that antivirus software provides to end users. Attackers can leverage this flaw to deliver malware through seemingly benign file types such as email attachments, web downloads, or system files, knowing that the target antivirus software will not properly scan these files for malicious content. The vulnerability creates a persistent threat vector that can be exploited across various attack surfaces, including email systems, web applications, and file sharing platforms. This issue aligns with CWE-20, which describes improper input validation, and demonstrates how insufficient validation of file signatures can lead to security bypass conditions. The attack pattern corresponds to techniques described in the MITRE ATT&CK framework under T1059 for command and scripting interpreter, as the malicious payloads can execute commands and scripts directly on compromised systems.
Mitigation strategies for this vulnerability require immediate patching of the ArcaVir 2005 software package to correct the file type interpretation logic and implement more robust signature validation mechanisms. Organizations should also implement additional layers of security controls including email filtering, web application firewalls, and behavioral monitoring systems to detect anomalous file execution patterns. The vulnerability highlights the importance of proper file format validation and the need for antivirus vendors to implement comprehensive file type detection algorithms that consider multiple factors beyond simple magic byte sequences. Security administrators should conduct thorough vulnerability assessments to identify systems running the affected software version and ensure that all endpoints are updated with the latest security patches. The incident underscores the necessity of maintaining up-to-date antivirus definitions and implementing defense-in-depth strategies that do not rely solely on signature-based detection methods, as demonstrated by the persistence of such vulnerabilities in legacy antivirus systems.