CVE-2006-5614 in Windows
Summary
by MITRE
Microsoft Windows NAT Helper Components (ipnathlp.dll) on Windows XP SP2, when Internet Connection Sharing is enabled, allows remote attackers to cause a denial of service (svchost.exe crash) via a malformed DNS query, which results in a null pointer dereference.
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Analysis
by VulDB Data Team • 04/25/2026
The vulnerability identified as CVE-2006-5614 affects Microsoft Windows operating systems, specifically Windows XP Service Pack 2 and later versions, when Internet Connection Sharing (ICS) is enabled. This issue resides within the Network Address Translation Helper components, more precisely in the ipnathlp.dll dynamic link library that manages the NAT functionality for network connections. The flaw manifests when the system processes malformed DNS queries that are transmitted through the ICS configuration, creating a condition that leads to system instability and service disruption.
The technical root cause of this vulnerability stems from improper input validation within the ipnathlp.dll module. When a malformed DNS query is received through the network interface configured for Internet Connection Sharing, the system fails to properly handle the malformed data structure, leading to a null pointer dereference condition. This programming error occurs because the code does not adequately check for valid pointer references before attempting to access memory locations, a classic example of a memory safety vulnerability that can be exploited through crafted network traffic. The vulnerability specifically impacts the svchost.exe process which hosts multiple Windows services including the NAT Helper service, causing the entire service to crash and restart.
The operational impact of CVE-2006-5614 represents a significant denial of service threat that can be exploited by remote attackers without requiring authentication or elevated privileges. An attacker can simply send a specially crafted DNS query to the affected Windows system to trigger the null pointer dereference, resulting in the immediate crash of the svchost.exe process that hosts the NAT Helper service. This disruption effectively breaks the Internet Connection Sharing functionality, rendering the affected system unable to properly route network traffic to other devices on the local network. The vulnerability aligns with CWE-476, which categorizes null pointer dereference issues as a common programming error that can lead to system instability and service disruption. From an adversarial perspective, this vulnerability can be classified under the MITRE ATT&CK framework as a Denial of Service technique, specifically targeting network services and system availability.
Mitigation strategies for this vulnerability primarily involve applying the official Microsoft security update released in response to this flaw, which patches the input validation error in the ipnathlp.dll component. Organizations should also implement network segmentation and access controls to limit exposure of systems running Internet Connection Sharing to untrusted networks. Network administrators can deploy intrusion detection systems to monitor for malformed DNS queries that may indicate exploitation attempts. Additionally, disabling Internet Connection Sharing on systems that do not require it provides a definitive workaround for environments where patching may be delayed or problematic. The vulnerability serves as a reminder of the importance of proper input validation in network services and demonstrates how seemingly minor programming errors in system components can have significant operational impacts. Organizations should also consider implementing network monitoring solutions that can detect and alert on unusual DNS query patterns that may indicate exploitation attempts against similar vulnerabilities in network infrastructure components.