CVE-2006-3787 in Personal Firewall
Summary
by MITRE
kpf4ss.exe in Sunbelt Kerio Personal Firewall 4.3.x before 4.3.268 does not properly hook the CreateRemoteThread API function, which allows local users to cause a denial of service (crash) and bypass protection mechanisms by calling CreateRemoteThread.
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Analysis
by VulDB Data Team • 01/02/2025
The vulnerability identified as CVE-2006-3787 affects Sunbelt Kerio Personal Firewall version 4.3.x prior to 4.3.268, specifically within the kpf4ss.exe component. This represents a critical security flaw that undermines the firewall's ability to properly monitor and control system activities. The issue stems from improper handling of the Windows API function CreateRemoteThread, which is fundamental to process manipulation and inter-process communication within the Windows operating system.
The technical flaw manifests in the kernel-level hooking mechanism implemented by the firewall's kpf4ss.exe module. When the system calls CreateRemoteThread, the firewall should intercept and analyze this operation to determine if it constitutes a potential security threat or unauthorized process manipulation. However, the vulnerable implementation fails to properly intercept or validate these API calls, creating a bypass opportunity for malicious actors. This improper hooking mechanism allows local users to exploit the firewall's monitoring capabilities by directly invoking CreateRemoteThread, which can lead to unpredictable system behavior.
The operational impact of this vulnerability is significant as it enables local users to both crash the firewall service and bypass its protection mechanisms simultaneously. When a local attacker successfully calls CreateRemoteThread against the firewall process, the system experiences a denial of service condition that can result in complete firewall failure. This crash effectively removes the network protection that users rely on, leaving their systems vulnerable to external threats. Additionally, the bypass capability means that attackers can circumvent the firewall's monitoring and control functions without detection, potentially allowing malicious code to execute without restriction.
The vulnerability aligns with CWE-119, which addresses improper restriction of operations within a limited error handling scope, and relates to the broader category of API hooking bypasses that have been documented in various security contexts. From an ATT&CK framework perspective, this vulnerability maps to techniques involving process injection and privilege escalation, as attackers can leverage the CreateRemoteThread API to manipulate protected processes. The attack vector specifically corresponds to T1055, which covers process injection techniques, and T1566, which deals with credential harvesting through various means including API manipulation.
Organizations should implement immediate mitigations including updating to Sunbelt Kerio Personal Firewall version 4.3.268 or later, which contains the necessary patch to properly handle CreateRemoteThread API calls. System administrators should also monitor for unauthorized local access attempts and consider implementing additional monitoring solutions that can detect anomalous API usage patterns. Network segmentation and privilege separation measures can help reduce the impact if exploitation occurs, while regular security assessments should verify that all firewall components are properly configured and updated. The vulnerability highlights the importance of proper API hooking implementation in security software and demonstrates how seemingly minor implementation flaws can result in significant security compromises.