CVE-1999-1223 in IIS
Summary
by MITRE
IIS 3.0 allows remote attackers to cause a denial of service via a request to an ASP page in which the URL contains a large number of / (forward slash) characters.
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Analysis
by VulDB Data Team • 04/20/2026
The vulnerability described in CVE-1999-1223 represents a classic denial of service weakness in Microsoft Internet Information Services version 3.0 that specifically targets the handling of Uniform Resource Locator requests containing excessive forward slash characters. This issue affects the ASP page processing functionality of IIS 3.0, creating a scenario where malicious actors can exploit the web server's request parsing mechanism to consume excessive system resources or trigger abnormal termination conditions. The flaw resides in how the server processes URLs with an unusually high number of consecutive forward slashes, which can cause the application server to enter an infinite loop or allocate excessive memory resources during the parsing phase.
The technical implementation of this vulnerability stems from inadequate input validation and boundary checking within the URL parsing component of IIS 3.0's web server engine. When an HTTP request containing an ASP page URL with numerous consecutive forward slash characters is processed, the server's internal URL decomposition routine fails to properly handle the malformed input. This weakness can be categorized under CWE-121, which addresses buffer overflow conditions, and more specifically aligns with CWE-400, representing unchecked resource consumption or denial of service vulnerabilities. The attack vector operates through the standard HTTP protocol where an attacker crafts a malicious URL containing hundreds or thousands of forward slashes, then submits this request to the target IIS 3.0 server.
From an operational perspective, this vulnerability can result in significant system degradation or complete service unavailability for legitimate users. The denial of service effect occurs because the server's processing resources become consumed in handling the malformed request, potentially causing the web server process to crash or become unresponsive. Network administrators may observe increased CPU utilization, memory consumption, or process starvation as the server attempts to parse the malformed URL. The impact extends beyond simple service interruption as it can affect other concurrent requests and potentially cause cascading failures in the web server's request handling pipeline. This vulnerability particularly affects organizations relying on older IIS 3.0 deployments that may not have received adequate security updates or patches.
The mitigation strategies for CVE-1999-1223 involve multiple layers of defensive measures that align with established cybersecurity frameworks including the MITRE ATT&CK methodology for defensive postures. Organizations should implement URL filtering mechanisms at the network perimeter through firewalls or web application firewalls that can detect and block requests containing excessive forward slash sequences. The most effective remediation approach involves upgrading to newer versions of IIS that have proper input validation and resource limits implemented in their URL parsing components. Additionally, administrators should configure resource limits and timeouts on web server processes to prevent indefinite resource consumption, and implement monitoring solutions that can detect unusual patterns in URL request processing that may indicate exploitation attempts. The vulnerability serves as an early example of how improper input validation can create exploitable conditions, emphasizing the importance of robust security practices in web server configurations and the necessity of keeping server software updated with security patches to prevent such denial of service scenarios.