CVE-2008-3373 in AVG
Summary
by MITRE
The files parsing engine in Grisoft AVG Anti-Virus before 8.0.156 allows remote attackers to cause a denial of service (engine crash) via a crafted UPX compressed file, which triggers a divide-by-zero error.
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Analysis
by VulDB Data Team • 05/26/2025
The vulnerability identified as CVE-2008-3373 represents a critical denial of service weakness within the Grisoft AVG Anti-Virus software suite, specifically affecting versions prior to 8.0.156. This flaw resides in the file parsing engine component responsible for analyzing and processing various file formats encountered during antivirus scanning operations. The vulnerability manifests when the system encounters a specially crafted UPX compressed file, which is a popular compression utility used to reduce executable file sizes while maintaining functionality. The attack vector leverages the decompression process within the antivirus engine, where the malicious file structure triggers an unexpected condition that leads to system instability.
The technical root cause of this vulnerability stems from inadequate input validation within the file parsing logic. When the AVG Anti-Virus engine attempts to decompress and analyze the crafted UPX file, it encounters a scenario that results in a divide-by-zero error during the decompression process. This mathematical operation produces an undefined result that causes the engine to crash and terminate unexpectedly. The vulnerability is classified under CWE-369 as a divide by zero error, which represents a fundamental programming flaw that can be exploited to disrupt service availability. The issue occurs at the intersection of file format handling and mathematical computation within the antivirus engine's processing pipeline, making it particularly dangerous as it can be triggered by simply opening or scanning a malicious file.
The operational impact of this vulnerability extends beyond simple service disruption, as it can be leveraged by remote attackers to systematically degrade the security posture of systems running vulnerable AVG versions. An attacker could craft malicious UPX compressed files that, when processed by the antivirus engine, would cause repeated crashes and system instability, effectively rendering the antivirus protection ineffective during critical threat detection periods. This creates a window of opportunity for additional attacks while simultaneously undermining user confidence in the security solution. The vulnerability demonstrates a classic case of insufficient error handling and input sanitization, where the software fails to properly validate compressed file structures before attempting mathematical operations on their contents. From an attacker perspective, this represents a low-effort, high-impact method of causing service disruption that aligns with ATT&CK technique T1499.004 for network denial of service, as it specifically targets the availability of security services.
Mitigation strategies for this vulnerability require immediate patch deployment to update AVG Anti-Virus to version 8.0.156 or later, which contains the necessary fixes to properly handle malformed UPX compressed files. System administrators should also implement additional defensive measures such as network-based file filtering to block known malicious UPX compressed files, and establish monitoring protocols to detect repeated engine crashes that may indicate exploitation attempts. The fix likely involves implementing proper input validation and error handling within the decompression routine to prevent division operations on zero values, along with enhanced logging capabilities to track suspicious file processing activities. Organizations should also consider implementing layered security approaches that do not rely solely on a single antivirus engine, as this vulnerability demonstrates the importance of having multiple defense mechanisms in place to prevent complete system compromise during such attacks.