CVE-2001-0239 in ISA Server
Summary
by MITRE
Microsoft Internet Security and Acceleration (ISA) Server 2000 Web Proxy allows remote attackers to cause a denial of service via a long web request with a specific type.
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Analysis
by VulDB Data Team • 10/07/2025
Microsoft Internet Security and Acceleration ISA Server 2000 presents a critical vulnerability that enables remote attackers to execute denial of service attacks through carefully crafted long web requests. This flaw specifically targets the web proxy functionality of the ISA Server 2000 platform, which serves as a crucial component for enterprise network security and traffic management. The vulnerability stems from inadequate input validation mechanisms within the proxy server's request processing pipeline, where the system fails to properly handle excessively long HTTP requests that contain specific formatting patterns.
The technical exploitation of this vulnerability occurs when an attacker submits a malformed web request that exceeds normal parameter limits within the ISA Server's proxy processing module. The server's insufficient buffer management and lack of proper request length validation cause the system to become unstable or crash entirely when processing these oversized requests. This behavior manifests as a complete service disruption, effectively preventing legitimate users from accessing web resources through the compromised proxy server. The vulnerability operates at the application layer of the network stack, making it particularly dangerous as it can be exploited from external networks without requiring authentication or privileged access.
From an operational impact perspective, this vulnerability poses significant risks to enterprise environments that rely on ISA Server 2000 for web traffic filtering and security management. Organizations may experience complete loss of web connectivity for their users, resulting in productivity losses and potential business disruption. The attack vector requires minimal technical expertise to execute, making it attractive to threat actors seeking to disrupt services without advanced hacking capabilities. Network administrators face the challenge of identifying and mitigating this vulnerability while maintaining continuous service availability, as the denial of service condition can persist until the server is manually restarted or the malformed request is properly filtered.
The underlying flaw aligns with CWE-122, which describes buffer overflow conditions in heap-based buffers, and demonstrates how improper input validation can lead to system instability. From an attack framework perspective, this vulnerability maps to the denial of service category within the MITRE ATT&CK framework, specifically under the technique of service disruption. Organizations should implement immediate mitigations including network-level filtering to block unusually long HTTP requests, deployment of intrusion detection systems to monitor for suspicious traffic patterns, and consideration of alternative proxy solutions. The vulnerability also highlights the importance of regular security updates and proper input sanitization practices in enterprise security infrastructure, emphasizing that legacy systems require ongoing security assessments to identify and address such critical weaknesses that can compromise entire network operations.