CVE-2001-0334 in IIS
Summary
by MITRE
FTP service in IIS 5.0 and earlier allows remote attackers to cause a denial of service via a wildcard sequence that generates a long string when it is expanded.
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Analysis
by VulDB Data Team • 10/07/2025
The vulnerability identified as CVE-2001-0334 represents a classic denial of service flaw affecting Microsoft Internet Information Services version 5.0 and earlier installations. This weakness specifically targets the File Transfer Protocol service component within IIS, which serves as a fundamental web server functionality for hosting and serving files over the internet. The vulnerability arises from insufficient input validation and string handling mechanisms within the FTP service implementation, creating a scenario where maliciously crafted wildcard sequences can trigger unexpected behavior in the server's processing pipeline.
The technical flaw manifests when the FTP service processes wildcard patterns that, upon expansion, generate excessively long strings that exceed the system's buffer capacity or processing limits. This occurs because the IIS FTP service fails to properly validate or limit the expansion of wildcard sequences, allowing attackers to craft requests that, when processed, cause the service to consume excessive memory resources or enter an infinite loop during string expansion operations. The vulnerability is particularly dangerous because it can be exploited remotely without requiring authentication, making it accessible to any attacker with network access to the target system. The flaw essentially creates a resource exhaustion condition where legitimate service operations become impossible due to the server's inability to handle the malformed requests properly.
The operational impact of this vulnerability extends beyond simple service disruption, as it can effectively render the entire FTP service unavailable to legitimate users while potentially causing system instability or crashes. Attackers can exploit this weakness to consume system resources rapidly, leading to complete service unavailability that can persist until the affected system is manually restarted or the malicious requests are filtered. The vulnerability affects organizations that rely on IIS 5.0 or earlier versions for their web hosting infrastructure, particularly those with public FTP services that are accessible to external users. This flaw demonstrates the critical importance of proper input validation and resource management in server applications, as it can be leveraged to create persistent availability issues that impact business operations and potentially compromise the overall security posture of the affected systems.
The vulnerability aligns with CWE-129, which addresses improper validation of length of input buffers, and represents a classic example of how insufficient input sanitization can lead to resource exhaustion attacks. From an ATT&CK framework perspective, this vulnerability maps to the T1499.004 technique related to network denial of service, where adversaries leverage service weaknesses to make systems unavailable to users. Organizations should implement immediate mitigations including applying the relevant Microsoft security patches, configuring proper input validation rules for FTP services, and implementing network-level filtering to block suspicious wildcard patterns. System administrators should also consider implementing monitoring solutions to detect unusual resource consumption patterns that may indicate exploitation attempts. The incident highlights the necessity of keeping server software updated and maintaining robust security configurations to prevent exploitation of known vulnerabilities that could otherwise provide attackers with persistent access to system resources and availability of critical services.