CVE-2001-0151 in IIS
Summary
by MITRE
IIS 5.0 allows remote attackers to cause a denial of service via a series of malformed WebDAV requests.
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Analysis
by VulDB Data Team • 10/08/2025
The vulnerability described in CVE-2001-0151 represents a critical denial of service weakness in Microsoft Internet Information Services version 5.0 that specifically targets the WebDAV (Web Distributed Authoring and Versioning) protocol implementation. This flaw enables remote attackers to disrupt service availability by submitting carefully crafted malformed requests that exploit inherent weaknesses in how IIS 5.0 processes WebDAV operations. The vulnerability operates at the application layer and demonstrates how protocol implementation flaws can be weaponized to compromise system availability, making it a significant concern for web server administrators and security professionals managing legacy systems.
The technical implementation of this vulnerability stems from insufficient input validation within the WebDAV extension of IIS 5.0. When the server receives malformed WebDAV requests containing malformed XML structures or improper request syntax, the processing engine fails to properly handle these malformed inputs, leading to system instability and eventual service termination. This type of vulnerability aligns with CWE-129, which addresses insufficient validation of length of input buffers, and CWE-20, which covers improper input validation. The flaw essentially creates a condition where the server's memory management and request processing routines become overwhelmed or corrupted by malformed data, causing the service to crash or become unresponsive to legitimate requests.
From an operational impact perspective, this vulnerability poses substantial risk to organizations relying on IIS 5.0 servers for web hosting services. Attackers can exploit this weakness to perform sustained denial of service attacks that render web applications inaccessible to legitimate users, potentially causing significant financial losses and reputational damage. The remote nature of the attack means that adversaries do not require physical access or local privileges to exploit the vulnerability, making it particularly dangerous in internet-facing environments. The impact extends beyond simple service disruption as it can affect multiple concurrent users and may require system restarts to restore normal operations, creating extended downtime periods that can last from minutes to hours depending on the severity of the exploitation.
Organizations should implement several mitigation strategies to address this vulnerability effectively. The primary recommendation involves applying the appropriate security patches released by Microsoft, which would include updating to IIS 5.0 Service Pack 3 or later versions that contain fixes for WebDAV processing. Network-level protections such as firewalls and intrusion detection systems can be configured to filter and monitor WebDAV traffic, though this approach may not prevent all exploitation attempts. Additionally, implementing rate limiting and request validation mechanisms can help reduce the impact of malformed requests. According to ATT&CK framework category T1498, this vulnerability falls under the Denial of Service technique, specifically targeting application availability. Organizations should also consider disabling WebDAV functionality entirely if it is not required for business operations, as this eliminates the attack surface associated with the vulnerable protocol implementation. The vulnerability serves as a historical example of how protocol-specific weaknesses can be exploited to compromise system availability, emphasizing the importance of proper input validation and robust error handling in server applications.