CVE-2001-0146 in Exchange
Summary
by MITRE
IIS 5.0 and Microsoft Exchange 2000 allow remote attackers to cause a denial of service (memory allocation error) by repeatedly sending a series of specially formatted URL s.
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Analysis
by VulDB Data Team • 10/08/2025
The vulnerability described in CVE-2001-0146 represents a classic denial of service flaw affecting Microsoft Internet Information Services version 5.0 and Microsoft Exchange 2000 Server. This vulnerability stems from insufficient input validation mechanisms within the web server's URL parsing functionality, creating a condition where malformed or specially crafted URLs can trigger memory allocation errors that ultimately lead to system unavailability. The flaw specifically manifests when the affected systems receive repeated requests containing malformed Uniform Resource Locator structures that exploit weaknesses in the URL processing pipeline.
The technical implementation of this vulnerability involves the exploitation of buffer handling mechanisms within the IIS web server component. When processing specially formatted URLs, the system fails to properly validate the length and structure of URL components, leading to memory allocation failures that can cause the web server process to crash or become unresponsive. This type of vulnerability falls under CWE-129, which describes improper validation of array indices, and more specifically aligns with CWE-121, concerning stack-based buffer overflow conditions. The flaw operates at the application layer and can be classified as a remote attack vector since it does not require local system access or authentication to exploit.
From an operational impact perspective, this vulnerability creates significant disruption for organizations relying on IIS 5.0 and Exchange 2000 servers. The denial of service condition can result in complete unavailability of web services and email functionality, potentially affecting thousands of users within an organization. The attack requires minimal sophistication and can be executed using readily available tools to send repeated malformed URL requests, making it particularly dangerous for production environments. Organizations may experience extended downtime while system administrators work to restore services and implement protective measures. The vulnerability directly impacts the availability component of the CIA triad, as it prevents legitimate users from accessing critical services.
The mitigation strategies for CVE-2001-0146 involve several layers of protection including immediate patching of affected systems with Microsoft security updates, implementing network-level filtering to block suspicious URL patterns, and configuring intrusion detection systems to monitor for unusual traffic patterns. Organizations should also consider implementing rate limiting mechanisms to prevent repeated requests from single sources and establish robust monitoring procedures to detect early signs of exploitation attempts. The ATT&CK framework categorizes this vulnerability under the T1499.004 technique for Network Denial of Service, which emphasizes the importance of protecting against resource exhaustion attacks. Additionally, implementing proper input validation at the application level and conducting regular security assessments can help prevent similar vulnerabilities from being exploited in the future.