CVE-1999-1222 in Windows
Summary
by MITRE
Netbt.sys in Windows NT 4.0 allows remote malicious DNS servers to cause a denial of service (crash) by returning 0.0.0.0 as the IP address for a DNS host name lookup.
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Analysis
by VulDB Data Team • 04/20/2026
The vulnerability described in CVE-1999-1222 resides within the Netbt.sys driver component of Windows NT 4.0 operating systems, specifically affecting the NetBIOS over TCP/IP implementation. This flaw represents a classic case of insufficient input validation where the system fails to properly handle malformed DNS responses. The vulnerability manifests when the Netbt.sys driver receives a DNS query response containing the special IP address 0.0.0.0, which typically indicates a failed or unspecified address resolution. This particular address format triggers an unhandled exception within the driver's processing logic, leading to system instability and eventual crash. The issue is particularly concerning because it can be exploited remotely through malicious DNS servers that deliberately respond with this invalid address, making it a significant denial of service threat.
The technical root cause of this vulnerability aligns with CWE-248, which describes "Uncaught Exception" in software systems where programs fail to handle exceptional conditions properly. The Netbt.sys driver lacks proper error handling mechanisms to process the 0.0.0.0 response, causing a null pointer dereference or similar memory access violation that results in kernel-level crashes. This behavior fits within the ATT&CK framework under the technique T1499.004 for "Endpoint Denial of Service" and specifically addresses the sub-technique involving network-based service disruption. The vulnerability operates at the network layer where DNS resolution occurs, making it a critical point of failure in the Windows NT 4.0 networking stack that affects all applications relying on NetBIOS name resolution.
From an operational impact perspective, this vulnerability creates a significant risk for Windows NT 4.0 systems deployed in enterprise environments where network reliability is paramount. The remote exploitation capability means that attackers can target systems without requiring local access or authentication, making it particularly dangerous in networked environments. When exploited successfully, the denial of service affects not only the immediate system but can potentially disrupt broader network services that depend on NetBIOS resolution. The impact extends beyond simple service interruption as the kernel crash can result in data loss, system reboots, and extended downtime for critical business applications that rely on stable network connectivity. Organizations running Windows NT 4.0 servers were particularly vulnerable since this operating system reached end-of-life support years before this vulnerability was widely recognized.
The mitigation strategies for this vulnerability primarily involve implementing network-level controls to prevent malicious DNS responses from reaching affected systems. Organizations should deploy DNS filtering mechanisms that can detect and block responses containing 0.0.0.0 addresses for NetBIOS name resolution queries. Additionally, implementing proper network segmentation and access controls can limit the attack surface for remote exploitation. Microsoft released patches for Windows NT 4.0 SP6 and later versions that addressed this specific vulnerability by improving input validation in the Netbt.sys driver. The recommended approach includes applying these security updates immediately and monitoring network traffic for suspicious DNS responses that might indicate attempts to exploit this flaw. System administrators should also implement network intrusion detection systems that can identify patterns consistent with this attack vector and establish baseline network behavior to detect anomalous DNS resolution patterns that could indicate exploitation attempts.