CVE-2001-0336 in IIS
Summary
by MITRE
The Microsoft MS00-060 patch for IIS 5.0 and earlier introduces an error which allows attackers to cause a denial of service via a malformed request.
If you want to get the best quality for vulnerability data then you always have to consider VulDB.
Analysis
by VulDB Data Team • 01/28/2025
The vulnerability described in CVE-2001-0336 represents a critical flaw in Microsoft Internet Information Services version 5.0 and earlier systems that was exposed during the implementation of the MS00-060 security patch. This particular issue emerged as a paradoxical consequence of the patching process itself, where the attempt to address one security concern inadvertently introduced a new vulnerability that could be exploited by malicious actors. The flaw specifically affects the handling of malformed HTTP requests within the IIS web server infrastructure, creating a scenario where legitimate system resources could be consumed or disrupted through carefully crafted malicious input. This vulnerability operates at the protocol level, targeting the core request processing mechanisms that govern how IIS interprets and responds to incoming web traffic from clients.
The technical implementation of this vulnerability stems from an error in the patching logic that was designed to resolve a different security issue within the IIS 5.0 platform. When the MS00-060 patch was applied to affected systems, it introduced a condition where certain malformed HTTP requests could trigger an improper handling routine within the web server's request parser. This error condition causes the IIS service to either enter a loop where it continuously processes the malformed request, or to crash entirely, resulting in a denial of service condition that prevents legitimate users from accessing the web server's resources. The vulnerability is particularly concerning because it affects the fundamental request processing capabilities of the web server, making it a high-impact issue that can effectively shut down web services without requiring advanced exploitation techniques. This flaw demonstrates the complexity involved in security patch management and the potential for well-intentioned security updates to introduce new attack vectors.
The operational impact of CVE-2001-0336 extends beyond simple service disruption to potentially compromise entire web infrastructure deployments that rely on IIS 5.0 or earlier versions. Organizations affected by this vulnerability face the risk of sustained denial of service attacks that could render their web applications inaccessible to legitimate users, resulting in business disruption and potential financial losses. The vulnerability's exploitation requires minimal technical skill, as attackers only need to send malformed HTTP requests to trigger the service disruption, making it particularly dangerous in environments where automated attack tools could be deployed. This type of vulnerability directly aligns with the attack pattern described in the MITRE ATT&CK framework under the denial of service category, specifically targeting the availability aspect of the CIA triad. The flaw also relates to CWE-129, which addresses improper input validation, and CWE-400, which covers unspecified denial of service conditions in software systems. Organizations that failed to properly test patches before deployment would find themselves in a particularly vulnerable position, as the patch intended to protect against one threat inadvertently created a new threat vector.
Mitigation strategies for this vulnerability require immediate action to either apply the corrected patch or implement alternative protective measures. Microsoft released updated patches specifically designed to address the error introduced by MS00-060, and organizations should prioritize applying these corrections to their affected systems. Network-level protections such as firewalls and intrusion detection systems can help filter malformed requests, though these measures are not foolproof and do not address the root cause. System administrators should also consider implementing request rate limiting and monitoring mechanisms to detect and respond to potential exploitation attempts. The incident highlights the critical importance of thorough testing procedures for security patches, particularly in production environments where the impact of flawed patches can be catastrophic. Organizations should establish robust patch management processes that include comprehensive testing in isolated environments before deployment to production systems, ensuring that security updates do not inadvertently introduce new vulnerabilities that could be exploited by adversaries. This vulnerability serves as a reminder of the complex interdependencies within system security and the necessity of careful evaluation of all security interventions to maintain overall system integrity.