CVE-1999-0225 in Windows
Summary
by MITRE
windows nt 4.0 allows remote attackers to cause a denial of service via a malformed smb logon request in which the actual data size does not match the specified size.
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Analysis
by VulDB Data Team • 04/17/2026
The vulnerability described in CVE-1999-0225 represents a critical denial of service flaw affecting Windows NT 4.0 systems that operate with Server Message Block protocol services. This issue manifests when the SMB logon request processing encounters a malformed packet where the declared data size differs from the actual data size contained within the message. The fundamental nature of this vulnerability stems from inadequate input validation mechanisms within the SMB protocol implementation, specifically during the authentication handshake process. Systems running Windows NT 4.0 are particularly susceptible because the operating system's SMB server component fails to properly validate the consistency between size fields and actual data payload in logon requests. This discrepancy creates a condition where the system's memory management routines become corrupted or enter an undefined state when attempting to process the malformed data structure, ultimately leading to system instability and complete service disruption. The vulnerability operates at the network protocol level and can be exploited remotely without requiring authentication credentials, making it particularly dangerous in networked environments where Windows NT 4.0 servers are exposed to untrusted networks.
The technical exploitation of this vulnerability occurs through the manipulation of SMB protocol packets during the authentication phase of network communication. When a client sends a malformed SMB logon request with inconsistent size parameters, the Windows NT 4.0 SMB server processes this request through its authentication subsystem, which attempts to allocate memory or process data structures based on the specified size field. However, when the actual data payload does not match the declared size, the server's memory management functions encounter a mismatch that can trigger buffer overflows, memory corruption, or invalid pointer dereferences. This type of vulnerability aligns with CWE-122, which describes buffer overflow conditions where insufficient validation occurs between declared and actual data sizes. The flaw essentially allows an attacker to manipulate the server's internal state by crafting packets that appear legitimate but contain malformed size fields, causing the system to process invalid data structures that ultimately result in system crashes or complete service termination. The vulnerability's remote exploitability means that attackers can trigger this condition from outside the local network, making it a significant threat to enterprise environments where Windows NT 4.0 servers are accessible to external networks.
The operational impact of CVE-1999-0225 extends beyond simple service disruption to potentially compromise entire network infrastructures that rely on Windows NT 4.0 servers for file sharing, print services, or authentication functions. When exploited successfully, the vulnerability can cause cascading failures as the affected server becomes unavailable, disrupting business operations and potentially creating denial of service conditions for legitimate users who depend on these services. The vulnerability affects the core SMB functionality that Windows NT 4.0 uses for network communication, meaning that any service relying on SMB authentication or file sharing protocols could be impacted. This includes file servers, print servers, and domain controllers that utilize the SMB protocol for their operations. The exploitability of this vulnerability aligns with ATT&CK technique T1499.004, which covers network denial of service attacks targeting SMB services. Organizations running Windows NT 4.0 systems were particularly vulnerable because the operating system was already in its later lifecycle phase, and Microsoft had not provided extensive updates or patches for this specific class of vulnerability. The impact could be severe for enterprises that had not migrated away from legacy Windows NT 4.0 infrastructure, as the service disruption could affect critical business operations and require significant downtime for recovery and system restoration.
Mitigation strategies for this vulnerability primarily involve implementing network segmentation and access control measures to prevent unauthorized remote access to Windows NT 4.0 servers. Organizations should consider disabling SMB services on systems that do not require file sharing functionality, and implementing network firewalls to restrict access to SMB ports 139 and 445 from untrusted networks. The most effective long-term solution involves migrating away from Windows NT 4.0 to supported operating systems that have proper input validation and memory management protections. For systems that must continue operating with Windows NT 4.0, implementing network monitoring and intrusion detection systems can help identify malformed SMB packets before they can cause service disruption. Additionally, applying any available security patches from Microsoft, though limited for this specific vulnerability, should be considered as part of a comprehensive security posture. Organizations should also implement regular system monitoring to detect unusual service behavior that might indicate exploitation attempts, and establish robust backup and recovery procedures to minimize downtime in case of successful attacks. The vulnerability serves as a historical example of how inadequate input validation in protocol implementations can create serious security risks, highlighting the importance of proper security testing and validation of network services.