CVE-2001-0546 in ISA Server
Summary
by MITRE
Memory leak in H.323 Gatekeeper Service in Microsoft Internet Security and Acceleration (ISA) Server 2000 allows remote attackers to cause a denial of service (resource exhaustion) via a large amount of malformed H.323 data.
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Analysis
by VulDB Data Team • 10/05/2025
The vulnerability described in CVE-2001-0546 represents a critical memory leak flaw within the H.323 Gatekeeper Service component of Microsoft Internet Security and Acceleration (ISA) Server 2000. This issue specifically targets the handling of H.323 protocol data, which is commonly used for signaling in voice over IP communications and multimedia conferences. The vulnerability exists in the way the ISA Server processes malformed H.323 data packets, creating a condition where memory allocated for processing these requests is not properly released back to the system. This memory management failure occurs during the parsing and validation of H.323 protocol messages, particularly those that contain malformed or unexpected data structures that do not conform to standard H.323 specifications.
The technical exploitation of this vulnerability enables remote attackers to perform a resource exhaustion attack by sending large volumes of malformed H.323 data to the affected ISA Server. Each malformed packet triggers the memory leak condition, causing the server to consume increasing amounts of available memory without proper cleanup. As the memory consumption grows progressively, the system eventually reaches a state where critical resources become depleted, leading to a complete denial of service condition that prevents legitimate users from accessing the server's services. The attack can be executed from any remote location without requiring authentication, making it particularly dangerous as it can be launched by anyone with network access to the vulnerable server.
The operational impact of this vulnerability extends beyond simple service disruption, as it can severely compromise the availability of communication services within organizations that rely on ISA Server for network security and voice communication infrastructure. Organizations using this server for H.323 traffic management, particularly those with voice over IP deployments, face significant risk of service interruptions that can affect business operations and communication capabilities. The memory leak affects the server's ability to handle legitimate H.323 requests, potentially causing cascading failures in voice communication systems and network infrastructure that depends on the ISA Server for traffic management. This vulnerability particularly impacts enterprises with extensive voice communication networks that utilize H.323 protocol standards for their multimedia conferencing and telephony services.
Security mitigations for this vulnerability primarily involve applying the official Microsoft security patches that address the memory leak in the H.323 Gatekeeper Service component. Organizations should also implement network segmentation strategies to limit exposure of the affected server to untrusted networks and consider deploying intrusion detection systems that can monitor for abnormal H.323 traffic patterns. Network administrators should establish monitoring protocols to detect unusual memory consumption patterns on ISA servers and implement automated alerting mechanisms to identify potential exploitation attempts. Additionally, organizations may need to consider implementing rate limiting or traffic filtering rules specifically targeting H.323 protocol traffic to prevent the exploitation of this vulnerability. This vulnerability aligns with CWE-401, which describes improper handling of memory allocation and deallocation, and represents a classic example of how protocol implementation flaws can create denial of service conditions that can be exploited remotely. The attack pattern follows ATT&CK technique T1499.004, which involves network disruption through resource exhaustion, making it a significant concern for enterprise security operations and incident response procedures.