CVE-2017-9977 in AVG
Summary
by MITRE
AVG AntiVirus for MacOS with scan engine before 4668 might allow remote attackers to bypass malware detection by leveraging failure to scan inside disk image (aka DMG) files.
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Analysis
by VulDB Data Team • 10/25/2019
The vulnerability identified as CVE-2017-9977 affects AVG AntiVirus for MacOS versions with scan engine prior to 4668, representing a critical flaw in endpoint protection software that undermines core security functionality. This weakness specifically targets the software's ability to properly analyze disk image files with the .dmg extension, which are commonly used on macOS systems for software distribution and installation. The vulnerability stems from an insufficient implementation of file scanning logic that fails to adequately process or examine the contents of disk image archives, creating a significant blind spot in the antivirus protection mechanism.
The technical flaw manifests as a failure within the scan engine's file traversal and analysis capabilities when encountering disk image files. When a DMG file is encountered during a system scan, the antivirus software does not properly mount or decompress the archive to examine its contents, instead treating the DMG file as a simple container without performing deep inspection of the files it contains. This behavior directly violates fundamental principles of antivirus scanning where all file types and containers must be thoroughly analyzed for potential threats. The issue is categorized under CWE-20 as "Improper Input Validation" and represents a failure in the software's security logic that allows malicious payloads hidden within disk images to evade detection.
The operational impact of this vulnerability is substantial as it provides attackers with a reliable method to bypass endpoint protection measures on macOS systems. Attackers can package malware within DMG files and deliver them to target systems without fear of detection by the affected AVG antivirus versions, effectively neutralizing the protection provided by the security software. This creates a dangerous scenario where legitimate users may unknowingly install malicious software through seemingly benign disk image downloads from the internet or other sources. The vulnerability particularly affects enterprise environments where macOS systems are commonly used and where antivirus protection is expected to provide comprehensive coverage against all potential attack vectors.
The attack surface for this vulnerability is particularly concerning given the widespread use of DMG files in macOS software distribution and the typical behavior of users who may not be aware of the security implications of mounting and executing software from disk images. The flaw enables attackers to leverage the trusted nature of disk image files to deliver malicious payloads that would otherwise be detected by proper antivirus scanning. This vulnerability aligns with ATT&CK technique T1059.007 for "Command and Scripting Interpreter: PowerShell" and T1070.004 for "Indicator Removal on Host: File Deletion" when considering the broader attack chain that could exploit such detection gaps. Organizations using affected AVG versions should immediately implement compensating controls including network-based detection, behavioral monitoring, and enhanced user education to mitigate the risk while applying the vendor-provided patch to resolve the underlying scanning engine flaw.
The remediation approach requires immediate deployment of the security update provided by AVG that addresses the scan engine's failure to properly process disk image files. This update should be prioritized across all affected systems and organizations should verify that the patch has been successfully applied through automated compliance monitoring. Additionally, system administrators should consider implementing network-based intrusion detection systems that can monitor for suspicious DMG file transfers and behaviors that might indicate malicious activity. The vulnerability highlights the importance of comprehensive testing of security software against common file formats and containers, particularly those that are native to specific operating systems. Organizations should also review their overall security posture to ensure that multiple layers of protection are in place, as relying solely on antivirus detection for containerized threats represents a significant risk that this vulnerability has exposed.