CVE-2003-0819 in ISA Server
Summary
by MITRE
Buffer overflow in the H.323 filter of Microsoft Internet Security and Acceleration Server 2000 allows remote attackers to execute arbitrary code in the Microsoft Firewall Service via certain H.323 traffic, as demonstrated by the NISCC/OUSPG PROTOS test suite for the H.225 protocol.
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Analysis
by VulDB Data Team • 07/21/2025
The vulnerability described in CVE-2003-0819 represents a critical buffer overflow flaw within the H.323 filtering component of Microsoft Internet Security and Acceleration Server 2000. This issue specifically targets the firewall service functionality that processes H.323 protocol traffic, which is commonly used in voice over IP communications and video conferencing systems. The vulnerability arises from insufficient input validation and boundary checking within the H.323 filter implementation, creating an exploitable condition that can be leveraged by remote attackers to gain unauthorized code execution privileges on the affected system.
The technical nature of this buffer overflow vulnerability falls under CWE-121, which classifies buffer overflow conditions where insufficient bounds checking allows attackers to overwrite adjacent memory locations. The flaw manifests when the Microsoft Firewall Service processes malformed H.323 traffic packets that conform to the H.225 protocol specifications used by the NISCC/OUSPG PROTOS test suite. This particular testing framework was designed to identify protocol implementation weaknesses in network security appliances and demonstrates how legitimate protocol traffic can be manipulated to trigger memory corruption conditions.
The operational impact of this vulnerability is severe as it allows remote attackers to execute arbitrary code with the privileges of the Microsoft Firewall Service process, typically running with elevated system permissions. This creates a significant attack surface for malicious actors who can potentially establish persistent access to the network infrastructure, escalate privileges, or use the compromised system as a launching point for further attacks within the network. The attack vector requires only the ability to send specially crafted H.323 traffic to the target server, making it particularly dangerous for organizations that rely on H.323 protocol support for their communication systems.
From an ATT&CK framework perspective, this vulnerability maps to multiple techniques including T1059.007 for command and scripting interpreter and T1068 for exploit for privilege escalation. The attack chain typically begins with reconnaissance to identify systems running Microsoft ISA Server 2000 with H.323 support, followed by crafting malicious protocol traffic that triggers the buffer overflow condition. The exploitation process leverages the standard buffer overflow technique of overwriting return addresses or function pointers to redirect execution flow to attacker-controlled code. Organizations should note that this vulnerability affects systems that may be operating in critical network infrastructure roles, making the potential impact on business continuity and security posture particularly concerning.
Mitigation strategies for CVE-2003-0819 include immediate deployment of Microsoft security patches released for ISA Server 2000, implementing network segmentation to limit exposure of vulnerable systems, and disabling H.323 protocol support where possible. Network administrators should also consider implementing intrusion detection systems that can identify anomalous H.323 traffic patterns and establish monitoring procedures for suspicious protocol behavior. The vulnerability highlights the importance of maintaining up-to-date security patches and proper protocol filtering configurations in network security infrastructure, particularly for legacy systems that may continue to support older communication protocols. Organizations should also review their overall network security posture and consider migrating to more modern security solutions that provide better protection against similar vulnerabilities in contemporary network environments.