CVE-2000-0226 is a vulnerability affecting Microsoft Internet Information Server (IIS) version 4.0, identified as a denial of service (DoS) issue caused by improper handling of large buffer requests in HTTP POST or PUT commands. Specifically, the vulnerability arises from the server's processing of chunked transfer encoding, where an attacker can send a request with a large buffer size that the IIS 4.0 server attempts to allocate in memory. This can lead to excessive memory consumption, resulting in resource exhaustion and ultimately causing the IIS service to become unresponsive or crash. The vulnerability is categorized as a buffer overflow related to chunked transfer encoding, but it does not appear to allow code execution or compromise confidentiality or integrity directly. The CVSS v2 score is 5.0 (medium severity), reflecting that the attack vector is network-based, requires no authentication, and impacts availability only. A patch addressing this vulnerability was released by Microsoft in security bulletin MS00-018. No known exploits have been reported in the wild, likely due to the age of the vulnerability and the obsolescence of IIS 4.0. However, unpatched legacy systems running IIS 4.0 remain susceptible to denial of service attacks leveraging this flaw.

For European organizations, the primary impact of this vulnerability is the potential disruption of web services hosted on IIS 4.0 servers. Although IIS 4.0 is an outdated product, some legacy systems may still be in operation within certain organizations, particularly in sectors with long system lifecycles such as government, manufacturing, or critical infrastructure. A successful exploitation would result in denial of service, causing downtime and loss of availability of affected web applications or services. This could interrupt business operations, degrade customer trust, and potentially impact compliance with service-level agreements or regulatory requirements related to availability. Since the vulnerability does not compromise data confidentiality or integrity, the risk is limited to service disruption. European organizations relying on IIS 4.0 in production environments should be aware that attackers can remotely trigger this DoS without authentication or user interaction, making it a straightforward attack vector if systems remain unpatched.

1. Immediate application of the official Microsoft patch provided in security bulletin MS00-018 to all IIS 4.0 servers is the most effective mitigation. 2. Organizations should conduct an inventory to identify any remaining IIS 4.0 instances and prioritize their upgrade or decommissioning, as IIS 4.0 is no longer supported and poses multiple security risks beyond this vulnerability. 3. Implement network-level protections such as web application firewalls (WAFs) or intrusion prevention systems (IPS) configured to detect and block unusually large or malformed HTTP POST or PUT requests that could exploit chunked transfer encoding buffer overflows. 4. Monitor IIS server logs and network traffic for abnormal request patterns indicative of attempted exploitation. 5. Where possible, migrate legacy web services to supported and actively maintained web server platforms to reduce exposure to known vulnerabilities. 6. Employ rate limiting and connection throttling to reduce the impact of potential DoS attempts targeting web servers.