CVE-2006-5939 in AVG Antivirus
Summary
by MITRE
Grisoft AVG Anti-Virus before 7.1.407 allows remote attackers to cause a denial of service (crash) via a crafted DOC file that triggers a divide-by-zero error. NOTE: some of these details are obtained from third party information.
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Analysis
by VulDB Data Team • 04/27/2026
The vulnerability identified as CVE-2006-5939 represents a critical divide-by-zero error in Grisoft AVG Anti-Virus versions prior to 7.1.407, demonstrating a classic software flaw that can be exploited for denial of service attacks. This issue manifests when the antivirus software processes a specially crafted Microsoft Word document file with specific characteristics that trigger arithmetic operations resulting in division by zero. The flaw exists within the document parsing and analysis routines of the antivirus engine, where the software fails to properly validate input data before performing mathematical operations. Such vulnerabilities fall under the CWE-369 weakness category, which specifically addresses divide-by-zero conditions that can lead to system instability and service disruption. The attack vector is particularly concerning as it requires no special privileges or authentication, making it accessible to remote threat actors who can simply send a malicious document to compromise the target system.
The operational impact of this vulnerability extends beyond simple service disruption to potentially compromise the overall security posture of systems relying on affected antivirus solutions. When the divide-by-zero error occurs, it causes the antivirus application to crash and terminate unexpectedly, leaving the system temporarily unprotected against malware threats. This creates a dangerous window where the system becomes vulnerable to attacks that could exploit the very protection mechanisms that were supposed to prevent them. The vulnerability demonstrates how defensive software can become a point of failure when not properly hardened against malformed input, creating a paradox where security tools themselves can be weaponized against the very systems they are designed to protect. From an attack perspective, this aligns with techniques described in the ATT&CK framework under the T1499 category, which covers network denial of service attacks that can be executed through manipulation of software components.
The technical implementation of this vulnerability stems from inadequate input validation within the document analysis subsystem of AVG Anti-Virus. When processing Microsoft Word documents, the software attempts to calculate certain metrics or perform analysis that involves division operations, but fails to properly check if the divisor is zero before executing the mathematical operation. This error in the software logic can be triggered by manipulating specific fields or metadata within the DOC file structure, causing the application to enter an undefined state and crash. The vulnerability affects the core functionality of the antivirus engine, specifically its ability to analyze and scan file content, which represents a fundamental security failure in the software architecture. Security researchers have noted that this type of error is particularly dangerous because it can be exploited in automated attack scenarios, where malicious actors could deploy scripts to send multiple crafted documents to systems running vulnerable versions, amplifying the potential impact of the attack.
Mitigation strategies for CVE-2006-5939 primarily focus on immediate software updates and patches provided by Grisoft, which address the underlying divide-by-zero condition in the document processing code. Organizations should prioritize upgrading to AVG Anti-Virus version 7.1.407 or later, which contains the necessary fixes to prevent the arithmetic error from occurring. Additionally, implementing network-based protections such as email filtering and content inspection can help prevent the delivery of malicious documents to vulnerable systems. Security teams should also consider deploying additional layers of protection including network segmentation and monitoring for unusual application behavior that might indicate exploitation attempts. The vulnerability underscores the importance of robust input validation and error handling in security software, as highlighted by industry best practices in secure coding standards. Organizations should also maintain comprehensive incident response procedures that account for potential service disruptions caused by such vulnerabilities, ensuring that alternative security measures remain active during patch deployment windows.