CVE-2000-0631 in IIS
Summary
by MITRE
An administrative script from IIS 3.0, later included in IIS 4.0 and 5.0, allows remote attackers to cause a denial of service by accessing the script without a particular argument, aka the "Absent Directory Browser Argument" vulnerability.
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Analysis
by VulDB Data Team • 05/31/2019
The CVE-2000-0631 vulnerability represents a critical denial of service flaw in Microsoft Internet Information Services versions 3.0 through 5.0 that stems from improper handling of directory browsing requests within administrative scripts. This vulnerability specifically affects the IIS directory browsing functionality where certain administrative scripts fail to properly validate input arguments when processing directory listing requests. The flaw exists in the way these scripts handle requests that lack the required directory argument, creating a condition where the system becomes unresponsive to legitimate requests.
The technical implementation of this vulnerability involves the administrative scripts that are part of the IIS web server administration toolkit. When these scripts receive a request for directory browsing without providing the expected directory argument, they enter an infinite loop or consume excessive system resources without proper error handling. The vulnerability manifests when attackers send specially crafted HTTP requests that omit the directory parameter that these administrative scripts typically require. This design flaw allows remote attackers to exploit the service by simply accessing the vulnerable script endpoint without supplying the necessary argument, causing the web server to become unresponsive or crash.
From an operational impact perspective, this vulnerability presents significant risks to organizations relying on IIS 3.0, 4.0, or 5.0 web servers. The denial of service condition can render entire web applications or entire server instances unavailable to legitimate users, potentially causing business disruption and financial losses. The vulnerability is particularly dangerous because it requires no authentication or specialized privileges to exploit, making it accessible to any remote attacker with basic network connectivity. The impact extends beyond simple service interruption as it can affect multiple concurrent users and may require manual intervention to restore normal service operations.
The vulnerability aligns with CWE-400, which categorizes improper handling of resources in computing systems, specifically addressing the lack of proper resource management and input validation. This weakness creates a condition where system resources are consumed inappropriately without proper bounds checking or error recovery mechanisms. From an attacker's perspective, this vulnerability maps to ATT&CK technique T1499.004, which involves network denial of service attacks through resource exhaustion. The attack vector is particularly effective because it targets administrative components that are typically accessible through standard web protocols, making it difficult to distinguish between legitimate administrative access and malicious exploitation attempts.
Mitigation strategies for this vulnerability include applying the appropriate Microsoft security patches that address the input validation issues in the administrative scripts, implementing network-level access controls to restrict access to administrative endpoints, and configuring proper resource limits on the web server to prevent resource exhaustion. Organizations should also consider implementing monitoring solutions that can detect anomalous access patterns to administrative scripts and establish incident response procedures for handling denial of service conditions. The most effective long-term solution involves upgrading to supported versions of IIS that have proper input validation and error handling mechanisms implemented to prevent similar vulnerabilities from occurring in future deployments.