CVE-2002-0072 in IIS
Summary
by MITRE
The w3svc.dll ISAPI filter in Front Page Server Extensions and ASP.NET for Internet Information Server (IIS) 4.0, 5.0, and 5.1 does not properly handle the error condition when a long URL is provided, which allows remote attackers to cause a denial of service (crash) when the URL parser accesses a null pointer.
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Analysis
by VulDB Data Team • 09/23/2025
The vulnerability described in CVE-2002-0072 represents a critical denial of service flaw within the web server infrastructure of Microsoft Internet Information Server versions 4.0, 5.0, and 5.1. This issue specifically affects the w3svc.dll ISAPI filter component that is integral to Front Page Server Extensions and ASP.NET functionality within IIS environments. The vulnerability stems from improper error handling mechanisms within the URL parsing subsystem, creating a scenario where maliciously crafted long URLs can trigger system instability and complete service disruption. This flaw operates at the core layer of web server request processing, making it particularly dangerous as it can be exploited through standard HTTP requests without requiring authentication or specialized privileges.
The technical implementation of this vulnerability involves a classic null pointer dereference condition within the URL parser logic of the w3svc.dll module. When the system encounters a URL exceeding normal length parameters, the error handling routine fails to properly validate memory references, leading to an access violation when the parser attempts to dereference a null pointer. This type of vulnerability is categorized as CWE-476 under the Common Weakness Enumeration framework, specifically addressing null pointer dereference issues that can lead to application crashes and system instability. The flaw manifests when the URL processing code assumes certain memory locations contain valid data without proper validation checks, creating an exploitable condition that can be triggered remotely through HTTP requests.
The operational impact of this vulnerability extends beyond simple service disruption to encompass broader security implications for web server availability and reliability. Attackers can exploit this weakness by sending specially crafted HTTP requests containing extremely long URLs to the target IIS server, causing the w3svc.dll module to crash and restart the web server service. This results in complete denial of service for legitimate users who cannot access the web applications hosted on the vulnerable system. The attack vector is particularly concerning because it requires minimal technical expertise to execute, making it a popular choice for automated denial of service attacks. The vulnerability affects not just individual web applications but the entire IIS service infrastructure, potentially disrupting multiple hosted websites and applications simultaneously.
Mitigation strategies for this vulnerability involve both immediate remediation actions and long-term architectural improvements to enhance system resilience. Microsoft released security patches for all affected IIS versions that properly handle URL length validation and implement robust error handling for malformed requests. Organizations should prioritize applying these security updates as a first line of defense, as they address the root cause of the null pointer dereference issue. Additional protective measures include implementing URL length restrictions at the web server configuration level, deploying intrusion detection systems to monitor for suspicious long URL patterns, and establishing proper input validation controls within application code. The vulnerability also highlights the importance of following secure coding practices such as those outlined in the OWASP Top Ten and CERT/CC secure coding guidelines, particularly regarding proper error handling and memory management. From an ATT&CK framework perspective, this vulnerability maps to the T1499.004 technique for network denial of service attacks, emphasizing the need for comprehensive defensive measures including proper system hardening and regular security assessments to prevent exploitation of such fundamental infrastructure flaws.