CVE-2006-5420 in WinRoute Firewall
Summary
by MITRE
Kerio WinRoute Firewall 6.2.2 and earlier allows remote attackers to cause a denial of service (crash) via malformed DNS responses.
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Analysis
by VulDB Data Team • 04/25/2026
The vulnerability identified as CVE-2006-5420 affects Kerio WinRoute Firewall versions 6.2.2 and earlier, presenting a critical security flaw that enables remote attackers to trigger a denial of service condition through the manipulation of DNS responses. This vulnerability resides within the firewall's DNS handling mechanisms, specifically in how the system processes incoming DNS packets that contain malformed or crafted responses. The flaw represents a classic buffer overflow or input validation issue that occurs when the firewall fails to properly sanitize or validate DNS response data before processing it within its network filtering infrastructure.
The technical implementation of this vulnerability demonstrates a failure in the firewall's DNS resolver component to properly validate incoming DNS packet structures and content. When a remote attacker crafts and sends malformed DNS responses to the vulnerable firewall, the system's DNS processing module attempts to parse these invalid packets without adequate boundary checking or input sanitization. This processing failure results in memory corruption that ultimately causes the firewall service to crash and terminate unexpectedly. The vulnerability operates at the application layer and leverages the firewall's legitimate DNS resolution capabilities to execute the attack, making it particularly insidious as it can be initiated through normal network traffic without requiring special privileges or direct system access.
From an operational impact perspective, this vulnerability severely compromises the availability and reliability of network security services provided by the affected firewall. Organizations relying on Kerio WinRoute Firewall for network protection face the risk of unexpected service outages that can disrupt business operations and leave networks exposed to potential attacks during the recovery period. The denial of service condition affects the firewall's ability to perform its primary function of network traffic filtering and monitoring, creating a security gap that attackers could exploit to bypass network protections. The vulnerability's remote exploitability means that attackers can initiate the attack from anywhere on the network without requiring physical access or authentication, making it particularly dangerous in enterprise environments where firewalls typically serve as critical security boundaries.
The flaw aligns with CWE-121, which describes heap-based buffer overflow conditions, and represents a classic example of insufficient input validation in network security appliances. This vulnerability also maps to ATT&CK technique T1498, which covers network denial of service attacks, and demonstrates how improperly handled network protocols can be leveraged to create service disruption. Organizations should implement immediate mitigations including applying the vendor-provided security patches, configuring firewall rules to limit DNS traffic from untrusted sources, and implementing monitoring systems to detect unusual DNS traffic patterns that might indicate exploitation attempts. Additionally, network segmentation strategies should be employed to limit the potential impact of such attacks, and regular security assessments should be conducted to identify similar vulnerabilities in other network security appliances within the organization's infrastructure.