CVE-2005-3374 in F-prot Antivirus
Summary
by MITRE
Multiple interpretation error in F-Prot 3.16c 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 vulnerability described in CVE-2005-3374 represents a critical file type interpretation flaw within F-Prot antivirus software version 3.16c that fundamentally undermines the security posture of endpoint protection systems. This issue stems from the software's improper handling of file magic bytes, specifically the MZ signature that traditionally identifies executable files. The flaw allows attackers to craft malicious files that appear harmless to the antivirus scanner while retaining executable capabilities, creating a dangerous misclassification that bypasses critical security controls.
The technical implementation of this vulnerability exploits the way F-Prot processes file headers and magic numbers during virus scanning operations. When a file containing the MZ magic byte sequence is encountered, the antivirus software incorrectly identifies it as a safe file type rather than a potential executable threat. This misclassification occurs because the scanner's file type detection logic fails to properly validate the complete file structure and content, instead relying solely on the initial magic byte signature. Attackers can leverage this weakness by creating compound files that combine multiple file types, such as the "triple headed" program mentioned in the description that contains EXE, EML, and HTML content within a single file structure.
The operational impact of this vulnerability extends beyond simple bypass of antivirus detection, creating a significant risk vector for end-user systems. When a malicious file is incorrectly classified as safe, it can be executed by applications on the end system without proper security scrutiny, potentially leading to arbitrary code execution, system compromise, and data exfiltration. The vulnerability particularly affects systems where users may open email attachments or execute downloaded files, as the EML and HTML components can trigger automatic execution paths within email clients or web browsers. This creates a multi-layered attack surface where the initial bypass of antivirus detection can lead to further exploitation through traditional attack vectors.
This vulnerability aligns with several cybersecurity frameworks and threat modeling concepts, including CWE-20, which addresses "Improper Input Validation" in software systems, and represents a classic example of how magic byte interpretation flaws can create security bypass opportunities. The ATT&CK framework categorizes this as a technique for "Exploitation for Defense Evasion" under the T1055 category, where attackers leverage software vulnerabilities to avoid detection mechanisms. The flaw also demonstrates characteristics of the principle of least privilege violation, as the system incorrectly grants elevated execution privileges to files that should be treated with heightened security scrutiny. Organizations affected by this vulnerability should implement immediate mitigations including software updates, enhanced file type validation, and comprehensive security awareness training to prevent exploitation of this critical weakness in their antivirus protection stack.
The remediation approach for this vulnerability requires immediate patching of F-Prot software to version 3.16d or later, which addresses the magic byte interpretation logic and properly validates file structures. Additionally, system administrators should implement layered security controls including email content filtering, web application firewalls, and enhanced endpoint detection and response capabilities to provide defense in depth against similar exploitation techniques. Regular security assessments and vulnerability scanning should be conducted to identify potential similar flaws in other security software components.