CVE-2001-0545 in IIS
Summary
by MITRE
IIS 4.0 with URL redirection enabled allows remote attackers to cause a denial of service (crash) via a malformed request that specifies a length that is different than the actual length.
Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.
Analysis
by VulDB Data Team • 10/05/2025
The vulnerability described in CVE-2001-0545 represents a classic buffer overflow condition affecting Microsoft Internet Information Services version 4.0 when configured with URL redirection functionality. This issue stems from inadequate input validation within the web server's request processing pipeline, specifically when handling HTTP requests that contain malformed content length specifications. The flaw occurs during the parsing of HTTP headers where the server fails to properly validate the relationship between the specified content length and the actual data received, creating a condition where maliciously crafted requests can trigger unexpected behavior in the application's memory management.
The technical implementation of this vulnerability leverages a fundamental weakness in the HTTP protocol handling mechanisms of IIS 4.0, where the server's response to malformed requests does not properly account for discrepancies between declared and actual data sizes. When a remote attacker crafts a request with a content length field that does not match the actual payload size, the web server's internal buffer management routines become corrupted, leading to memory corruption that ultimately results in application termination. This type of vulnerability falls under the CWE-121 category of stack-based buffer overflow, though it manifests in a more complex manner due to the HTTP request processing context and the specific interaction with URL redirection features.
From an operational perspective, this vulnerability presents a significant risk to organizations relying on IIS 4.0 servers for web hosting services, as it can be exploited to perform denial of service attacks without requiring authentication or elevated privileges. The impact extends beyond simple service disruption, as the crash condition can potentially be leveraged to cause system instability or even facilitate more sophisticated attacks if combined with other vulnerabilities. The vulnerability is particularly concerning in environments where continuous availability is critical, as a single malicious request can bring down entire web applications or services. The attack vector is relatively simple to execute, requiring only basic HTTP request crafting capabilities and making it accessible to attackers with minimal technical expertise.
Organizations should implement immediate mitigations including disabling URL redirection functionality when not required, applying the appropriate Microsoft security patches, and implementing network-level protections such as firewall rules that restrict access to potentially vulnerable endpoints. The vulnerability aligns with ATT&CK technique T1499.004 for network denial of service, and organizations should consider implementing intrusion detection systems to monitor for suspicious HTTP request patterns that may indicate exploitation attempts. Additionally, regular security assessments should verify proper configuration of web server components and ensure that all known vulnerabilities are addressed through timely patch management processes. The incident highlights the importance of proper input validation and robust error handling in web server implementations, particularly in legacy systems that may not have been designed with modern security considerations in mind.