CVE-1999-0281 is a vulnerability affecting Microsoft Internet Information Server (IIS) versions 2.0 and 3.0, which were released in the mid-1990s. The vulnerability allows an attacker to cause a denial of service (DoS) condition by sending HTTP requests with excessively long URLs. IIS in these versions does not properly handle or limit the length of the URL in incoming requests, leading to resource exhaustion or server instability. This can cause the web server to crash or become unresponsive, denying legitimate users access to hosted web services. The vulnerability does not impact confidentiality or integrity but solely affects availability. Exploitation requires no authentication and can be performed remotely over the network, making it relatively easy to attempt. However, these IIS versions are extremely outdated and no longer supported or commonly used in modern environments. No patches are available for this vulnerability, and there are no known exploits actively used in the wild. The CVSS v2 score is 5.0 (medium severity), reflecting the ease of exploitation and impact on availability without affecting confidentiality or integrity.

For European organizations, the direct impact of this vulnerability today is minimal due to the obsolescence of IIS versions 2.0 and 3.0. Most enterprises and public sector entities have long since migrated to newer, supported web server software. However, legacy systems or industrial control environments that have not been updated might still run these versions, especially in isolated or specialized networks. In such cases, an attacker could remotely disrupt web services by sending long URL requests, causing denial of service and potential operational disruptions. This could affect internal portals, legacy applications, or monitoring systems relying on IIS 2.0/3.0. Given the lack of patches, mitigation relies on network-level controls and isolation. The vulnerability does not expose sensitive data or allow code execution, so the risk is confined to service availability. Organizations in sectors with legacy infrastructure, such as manufacturing or utilities, should be particularly cautious.

Since no patches are available for IIS 2.0 and 3.0, European organizations should prioritize upgrading to supported versions of IIS or alternative modern web servers. If upgrading is not immediately feasible, network-level mitigations are critical. Implement strict input validation and URL length restrictions on perimeter firewalls or web application firewalls (WAFs) to block requests with abnormally long URLs before they reach the IIS server. Deploy intrusion detection/prevention systems (IDS/IPS) configured to detect and block anomalous HTTP traffic patterns indicative of this attack. Isolate legacy IIS servers from public internet access by placing them behind VPNs or internal networks with restricted access. Regularly monitor server logs for unusual request patterns and conduct vulnerability assessments to identify legacy IIS deployments. Finally, develop incident response plans to quickly address potential DoS events targeting these legacy systems.