CVE-2002-2161 in Personal Firewall
Summary
by MITRE
Kerio Personal Firewall (KPF) 2.1.4 and earlier allows remote attackers to cause a denial of service (hang and CPU consumption) via a SYN packet flood.
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Analysis
by VulDB Data Team • 07/11/2024
Kerio Personal Firewall version 2.1.4 and earlier implementations contain a critical vulnerability that enables remote attackers to execute denial of service attacks through SYN packet flooding techniques. This vulnerability represents a fundamental flaw in the firewall's packet processing logic where the system fails to properly handle excessive SYN requests, leading to system instability and resource exhaustion. The flaw manifests when the firewall receives a high volume of SYN packets without proper completion of the TCP three-way handshake process, causing the system to consume excessive CPU cycles while attempting to process these malformed connections. This vulnerability directly impacts the availability aspect of the information security triad by rendering the firewall ineffective and potentially causing complete system hang conditions that prevent legitimate network traffic from being processed. The technical implementation of this vulnerability aligns with common denial of service attack patterns where attackers exploit protocol implementation weaknesses to exhaust system resources. This flaw is categorized under CWE-400 as unspecified resource exhaustion, which occurs when a system fails to properly manage resource allocation during network traffic processing. The attack vector operates through the network layer where malicious actors can send a large number of SYN packets to the firewall's listening ports without completing the TCP handshake, creating a condition where the firewall continuously processes these incomplete connection requests. From an operational standpoint, this vulnerability can be exploited using standard network tools such as hping or custom scripts that generate SYN flood attacks against the targeted firewall system. The impact extends beyond simple service disruption as the firewall may become unresponsive to legitimate traffic while simultaneously consuming significant CPU resources that could affect overall system performance. The vulnerability affects both the local system's ability to maintain network connectivity and the firewall's capacity to provide security services to the networked environment. According to ATT&CK framework, this vulnerability maps to T1498 as a network denial of service attack, where the adversary leverages system weaknesses to disrupt services. The root cause of this vulnerability lies in inadequate input validation and resource management within the firewall's TCP connection handling mechanisms. The system fails to implement proper rate limiting or connection tracking controls that would normally prevent such resource exhaustion scenarios. Attackers can exploit this by sending a sustained flood of SYN packets to specific ports, causing the firewall to allocate memory and processing cycles to track these incomplete connections indefinitely. This creates a cascading effect where legitimate connection attempts are delayed or dropped while the firewall becomes increasingly unresponsive to normal network traffic. The vulnerability demonstrates a critical design flaw in the firewall's connection state management where incomplete TCP handshakes are not properly timed out or discarded. The impact of this vulnerability can be severe for organizations relying on Kerio Personal Firewall for network security, as it directly compromises the firewall's ability to provide essential security services. Organizations may experience complete network outages or significant degradation of network performance while the firewall attempts to process the flood of malformed packets. The vulnerability also highlights the importance of proper resource management and input validation in network security appliances. Network administrators should consider implementing additional network-level protections such as SYN cookies or rate limiting at the network perimeter to mitigate the risk of exploitation. The recommended mitigation strategies include upgrading to Kerio Personal Firewall versions that address this vulnerability, implementing network-based rate limiting controls, and deploying additional security monitoring to detect unusual traffic patterns that may indicate SYN flood attacks. Organizations should also consider implementing intrusion detection systems that can identify and alert on unusual SYN packet patterns. The vulnerability serves as a reminder of the critical importance of proper resource management in security appliances and the need for robust input validation to prevent resource exhaustion attacks that can compromise system availability.