CVE-1999-0867 in IIS
Summary
by MITRE
Denial of service in IIS 4.0 via a flood of HTTP requests with malformed headers.
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Analysis
by VulDB Data Team • 12/01/2024
The vulnerability described in CVE-1999-0867 represents a classic denial of service attack targeting Microsoft Internet Information Services version 4.0. This flaw specifically exploits the web server's handling of HTTP requests that contain malformed headers, creating a condition where the server becomes overwhelmed and unable to process legitimate requests. The vulnerability emerged during a period when web servers were rapidly evolving to handle increasing traffic loads, yet many implementations still contained fundamental flaws in their request parsing and validation mechanisms. The attack vector involves flooding the target server with carefully crafted HTTP requests that contain headers structured in ways that trigger unexpected behavior within the IIS 4.0 processing pipeline.
The technical implementation of this vulnerability stems from inadequate input validation within the HTTP request processing module of IIS 4.0. When the web server encounters HTTP requests with malformed headers, the parsing logic fails to properly handle these edge cases, leading to resource exhaustion or process crashes. This behavior can be categorized under CWE-129 Input Validation and Output Encoding, specifically relating to insufficient validation of input data. The flaw manifests when the server attempts to process headers that do not conform to standard HTTP specifications, causing the application to enter an error state or consume excessive system resources. The vulnerability is particularly dangerous because it can be executed with minimal technical expertise and can be easily automated, making it a preferred method for attackers seeking to disrupt web services.
The operational impact of CVE-1999-0867 extends beyond simple service disruption to potentially affecting business continuity and customer satisfaction. Organizations relying on IIS 4.0 for their web hosting services would experience complete service unavailability during an attack, leading to financial losses and reputational damage. The vulnerability affects the fundamental availability aspect of the CIA triad, as it prevents legitimate users from accessing web resources. Attackers can leverage this vulnerability to perform distributed denial of service attacks by coordinating multiple systems to flood the target server simultaneously, amplifying the impact of the attack. The low complexity and high impact nature of this vulnerability made it particularly attractive to malicious actors during the late 1990s when web infrastructure was still maturing and security practices were not yet well-established.
Mitigation strategies for this vulnerability include implementing rate limiting and connection throttling mechanisms to prevent flooding attacks from overwhelming the server. Organizations should deploy intrusion detection systems that can identify and block malformed HTTP requests before they reach the web server. The most effective solution involves upgrading to newer versions of IIS that contain proper input validation and error handling mechanisms. Additionally, implementing proper network security controls such as firewalls with HTTP inspection capabilities can help filter out malicious requests. According to ATT&CK framework, this vulnerability maps to T1498 Exploitation for Denial of Service, where adversaries leverage software weaknesses to disrupt services. System administrators should also consider implementing web application firewalls and configuring the server to drop requests with suspicious header patterns, as recommended in industry best practices for securing web infrastructure against common attack vectors.