CVE-2019-3973 in Comodo
Summary
by MITRE
Comodo Antivirus versions 11.0.0.6582 and below are vulnerable to Denial of Service affecting CmdGuard.sys via its filter port "cmdServicePort". A low privileged process can crash CmdVirth.exe to decrease the port's connection count followed by process hollowing a CmdVirth.exe instance with malicious code to obtain a handle to "cmdServicePort". Once this occurs, a specially crafted message can be sent to "cmdServicePort" using "FilterSendMessage" API. This can trigger an out-of-bounds write if lpOutBuffer parameter in FilterSendMessage API is near the end of specified buffer bounds. The crash occurs when the driver performs a memset operation which uses a size beyond the size of buffer specified, causing kernel crash.
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Analysis
by VulDB Data Team • 11/01/2023
Comodo Antivirus version 11.0.0.6582 and earlier contains a critical denial of service vulnerability in the CmdGuard.sys kernel driver component that affects the cmdServicePort filter port. This vulnerability stems from inadequate input validation within the FilterSendMessage API implementation, creating a dangerous condition where maliciously crafted messages can trigger kernel-level crashes. The flaw exists in the driver's handling of buffer boundaries during memory operations, specifically when processing messages sent through the cmdServicePort interface. The vulnerability is particularly concerning because it can be exploited by low privileged processes, making it accessible to attackers without requiring administrative privileges or elevated system access. This represents a significant security weakness in the antivirus protection stack where the very component designed to defend against malware can be turned against the system itself.
The technical exploitation of this vulnerability begins with a low privileged process that crashes the CmdVirth.exe service to reduce the port's connection count, followed by process hollowing techniques to replace a legitimate CmdVirth.exe instance with a malicious one. This malicious process then obtains a handle to the cmdServicePort, allowing it to send specially crafted messages through the FilterSendMessage API. The vulnerability manifests when the lpOutBuffer parameter in FilterSendMessage is positioned near the end of the specified buffer boundaries, causing an out-of-bounds write condition. The kernel crash occurs during a memset operation where the size parameter exceeds the actual buffer size, leading to memory corruption and system instability. This type of vulnerability aligns with CWE-121, which describes stack-based buffer overflow conditions, and CWE-787, which covers out-of-bounds write vulnerabilities. The exploitation technique demonstrates a sophisticated understanding of Windows kernel driver behavior and memory management patterns.
The operational impact of this vulnerability extends beyond simple denial of service, as it can lead to complete system instability and potential privilege escalation opportunities. When the kernel crashes due to the out-of-bounds write condition, it can cause system-wide instability that affects other security services and potentially allows attackers to bypass security controls. The vulnerability's exploitation path creates a persistent threat vector that can be maintained across system reboots, as the malicious CmdVirth.exe replacement can be designed to survive normal system operations. From an ATT&CK framework perspective, this vulnerability maps to T1055.001 (Process Injection) and T1068 (Local Privilege Escalation) techniques, as it enables attackers to inject code into protected processes and potentially elevate their privileges. The vulnerability also represents a failure in the principle of least privilege, as a low privileged user can exploit kernel-level components to cause system-wide disruptions.
Mitigation strategies for this vulnerability must address both immediate remediation and long-term security hardening. The most effective immediate solution is to update to Comodo Antivirus version 11.0.0.6583 or later, which contains patches addressing the buffer overflow condition in the CmdGuard.sys driver. System administrators should also implement process monitoring to detect anomalous CmdVirth.exe behavior and unauthorized process hollowing attempts. Network segmentation and access controls can limit the potential impact of such vulnerabilities by restricting access to systems running vulnerable antivirus software. Additionally, implementing kernel-mode driver verification and monitoring can help detect and prevent exploitation attempts. The vulnerability highlights the importance of proper input validation in kernel drivers and demonstrates how seemingly minor buffer handling issues can lead to catastrophic system failures. Organizations should also consider implementing behavioral monitoring solutions that can detect the specific exploitation patterns associated with this vulnerability, including unusual process creation sequences and memory manipulation activities.