CVE-2001-0547 in ISA Server
Summary
by MITRE
Memory leak in the proxy service in Microsoft Internet Security and Acceleration (ISA) Server 2000 allows local attackers to cause a denial of service (resource exhaustion).
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Analysis
by VulDB Data Team • 10/05/2025
The vulnerability identified as CVE-2001-0547 represents a critical memory leak flaw within Microsoft Internet Security and Acceleration (ISA) Server 2000 proxy service component. This issue manifests as a resource exhaustion condition that can be exploited by local attackers to execute denial of service attacks against the target system. The vulnerability specifically affects the proxy service functionality that handles network traffic forwarding and filtering operations within the ISA Server environment.
The technical implementation of this memory leak occurs within the proxy service's memory management routines where allocated memory blocks are not properly released back to the system after processing network requests. This flaw is categorized under CWE-401 as improper management of dynamic memory, specifically manifesting as a memory leak condition. When the proxy service processes incoming requests, it allocates memory for request handling, response processing, and connection management but fails to consistently deallocate these resources when they are no longer needed. The cumulative effect of these unclaimed memory segments gradually consumes available system memory resources over time.
The operational impact of CVE-2001-0547 extends beyond simple resource exhaustion to potentially compromise the entire ISA Server infrastructure. As memory consumption increases, the system experiences performance degradation, application slowdowns, and eventually complete service unavailability. Local attackers can exploit this vulnerability by repeatedly submitting proxy requests that trigger the memory allocation without corresponding deallocation, causing the system to consume all available memory resources. This attack vector aligns with ATT&CK technique T1499.004 for resource exhaustion attacks and represents a classic example of how memory management flaws can be leveraged for denial of service operations.
The vulnerability's exploitation requires local system access, making it particularly concerning for environments where privileged accounts are compromised or where insider threats exist. The impact is severe as it can render the entire ISA Server operational, affecting all network traffic that relies on the proxy service for filtering, caching, and security enforcement. Organizations running ISA Server 2000 are particularly vulnerable since this version predates many modern memory management improvements and security hardening features. The memory leak can be triggered through normal proxy service operations, making detection difficult and allowing attackers to maintain persistent resource exhaustion conditions without raising immediate alarms.
Mitigation strategies for CVE-2001-0547 should include immediate implementation of Microsoft security patches and updates for ISA Server 2000, along with comprehensive monitoring of system memory usage patterns. System administrators should establish baseline memory consumption metrics and implement automated alerting for unusual memory usage trends. Network segmentation and access control measures can help limit local access privileges to reduce exploitation potential. Additionally, implementing regular system restart procedures and memory cleanup routines can provide temporary relief while permanent patches are deployed. Organizations should also consider upgrading to newer versions of ISA Server or alternative security solutions that have addressed these memory management vulnerabilities. The remediation process should include thorough testing of patches in controlled environments to ensure compatibility with existing network infrastructure and security policies.