CVE-2001-1533 in ISA Server
Summary
by MITRE
** DISPUTED * Microsoft Internet Security and Acceleration (ISA) Server 2000 allows remote attackers to cause a denial of service via a flood of fragmented UDP packets. NOTE: the vendor disputes this issue, saying that it requires high bandwidth to exploit, and the server does not experience any instability. Therefore this "laws of physics" issue might not be included in CVE.
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Analysis
by VulDB Data Team • 01/16/2025
The vulnerability described in CVE-2001-1533 relates to Microsoft Internet Security and Acceleration ISA Server 2000, a network security solution designed to protect corporate networks from external threats. This particular issue involves a potential denial of service condition that could be triggered by sending a large volume of fragmented UDP packets to the target server. The vulnerability is classified as disputed by the vendor, indicating that Microsoft has not officially recognized this as a security flaw within their product.
The technical flaw centers on how ISA Server 2000 handles fragmented UDP packets, which represent a fundamental aspect of network communication where large packets are broken into smaller fragments for transmission across networks. When these fragmented packets are sent in high volumes to the server, they can potentially overwhelm the system's processing capabilities or trigger resource exhaustion conditions. This type of attack falls under the category of resource exhaustion attacks that aim to make services unavailable to legitimate users by consuming system resources.
From an operational impact perspective, the vulnerability could theoretically lead to service disruption for organizations relying on ISA Server 2000 for their network security infrastructure. However, Microsoft's official stance that the issue requires high bandwidth to exploit and does not cause server instability suggests that the practical impact may be limited. The vendor's position indicates that normal network traffic patterns would not typically trigger this condition, making it more of a theoretical concern than an immediate operational threat.
The disputed nature of this CVE aligns with certain principles outlined in the Common Weakness Enumeration framework where some issues may not meet the criteria for official vulnerability classification. This particular case demonstrates how network-level behaviors can be interpreted differently by vendors, with some considering certain resource consumption patterns as expected network behavior rather than security flaws. The issue also relates to the broader ATT&CK framework's concept of resource exhaustion attacks, though the specific classification may vary based on vendor interpretation and practical exploitability.
Organizations using ISA Server 2000 should consider implementing network monitoring solutions to detect unusual packet patterns and maintain adequate bandwidth capacity to handle potential traffic spikes. The vendor's position that this requires high bandwidth to exploit suggests that typical network environments may not be vulnerable to this specific condition, but network administrators should still maintain awareness of unusual traffic patterns that could indicate attempted exploitation of any potential weaknesses in their security infrastructure.