CVE-2005-3214 in Avast Antivirus
Summary
by MITRE
Multiple interpretation error in unspecified versions of Avast Antivirus allows remote attackers to bypass virus detection via a malicious executable in a specially crafted RAR file with malformed central and local headers, which can still be opened by products such as Winrar and PowerZip, even though they are rejected as corrupted by Winzip and BitZipper.
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Analysis
by VulDB Data Team • 07/26/2017
The vulnerability described in CVE-2005-3214 represents a critical flaw in Avast Antivirus software that demonstrates the complexity of file format parsing and the potential for security bypass through seemingly innocuous file manipulation techniques. This issue specifically targets the way antivirus software interprets archive files, particularly RAR format archives that contain malicious executables. The vulnerability exploits a fundamental weakness in how Avast processes and validates RAR file structures, creating a scenario where legitimate archive viewers like Winrar and PowerZip can successfully open and extract files while Avast fails to properly detect the malicious content within the same archive. This discrepancy in interpretation creates a significant security gap that attackers can leverage to evade detection mechanisms.
The technical root cause of this vulnerability lies in the improper handling of malformed RAR central and local headers, which are integral components of the RAR file format specification. When a RAR archive contains specially crafted headers that deviate from standard specifications, Avast's parsing logic fails to properly validate these structures, allowing malicious payloads to be hidden within the archive. The vulnerability operates at the level of file format interpretation rather than network protocol handling, making it particularly insidious as it can bypass traditional network-based detection methods. This type of error falls under the CWE-129 category of Improper Validation of Array Index, though it manifests specifically in the context of archive file parsing where header validation fails to properly sanitize input data.
The operational impact of this vulnerability extends beyond simple detection bypass, as it fundamentally undermines the trust model that antivirus software provides to users. When legitimate archive viewers can successfully process files that antivirus systems reject as corrupted, it creates confusion and potentially leads to users bypassing security warnings or assuming that files are safe when they are not. Attackers can exploit this by creating RAR files that appear normal to standard archive tools but contain malicious executables that evade detection by Avast. This creates a scenario where the antivirus software becomes less effective at protecting users, particularly in environments where RAR archives are commonly used for file distribution.
The implications of this vulnerability align with several ATT&CK framework techniques including T1059.007 for Command and Scripting Interpreter and T1204.002 for User Execution, as the malicious files can be executed through normal archive extraction processes. Organizations relying on Avast for protection may experience false negatives where malicious files are not detected despite being present in their systems. The vulnerability also demonstrates the importance of consistent validation across different software tools, as the fact that Winzip and BitZipper reject the same files while Winrar and PowerZip accept them suggests a fundamental inconsistency in how different tools interpret the same malformed data. This inconsistency represents a broader challenge in cybersecurity where different implementations of the same file format can create security gaps that attackers can exploit.
Mitigation strategies for this vulnerability should include immediate software updates from Avast to address the parsing logic flaws, along with implementing additional validation layers beyond traditional antivirus detection. Network administrators should consider implementing additional file validation checks for RAR archives, particularly those that are received from untrusted sources. The vulnerability highlights the need for comprehensive testing of file format parsers and the importance of maintaining consistent behavior across different software implementations. Organizations should also consider implementing sandboxing techniques for archive extraction processes and maintaining multiple layers of detection to ensure that even if one system fails to detect malicious content, other security measures can provide coverage. Regular security audits of file handling components and adherence to secure coding practices that prevent improper validation of input data should be implemented as part of broader cybersecurity hygiene measures.