CVE-1999-1544 is a buffer overflow vulnerability found in the FTP server component of Microsoft Internet Information Server (IIS) versions 3.0 and 4.0. This vulnerability arises when the FTP server processes an excessively long NLST (list) command, which can cause the server to overflow its buffer. The overflow can lead to a denial of service (DoS) condition, crashing the FTP service and potentially affecting the availability of the IIS server. The vulnerability can be exploited remotely without authentication, as the FTP service typically listens on a network port accessible to external users. However, exploitation success may vary depending on the environment and configuration, with some cases requiring local access. The vulnerability does not impact confidentiality or integrity directly but affects availability by causing service disruption. No patches are available for this vulnerability, and there are no known exploits in the wild documented. The CVSS v2 score is 5.0 (medium severity), reflecting the ease of remote exploitation and the impact limited to availability. Given the age of the affected IIS versions (released in the late 1990s), modern systems are unlikely to be affected unless legacy systems remain in operation. The vulnerability highlights the risks of buffer overflows in network-facing services and the importance of maintaining updated software versions.

For European organizations, the primary impact of CVE-1999-1544 is the potential denial of service on IIS FTP servers running versions 3.0 or 4.0. This could disrupt file transfer operations critical for business processes, especially in organizations relying on legacy systems for FTP-based workflows. Although the vulnerability does not allow data theft or modification, the service disruption can affect operational continuity, leading to downtime and potential financial losses. Organizations in sectors with legacy infrastructure, such as manufacturing, government agencies, or utilities, might be more vulnerable if they have not upgraded from these outdated IIS versions. The lack of available patches means organizations must rely on alternative mitigations or system upgrades. Given the age of the vulnerability, the risk is generally low for most modern European enterprises but remains relevant for those maintaining legacy IIS FTP servers.

Since no official patches are available for this vulnerability, European organizations should prioritize upgrading from IIS versions 3.0 and 4.0 to supported, modern versions of IIS or alternative FTP server software that receive security updates. If upgrading is not immediately feasible, organizations should consider disabling the FTP service on IIS to eliminate exposure. Network-level mitigations such as firewall rules restricting access to the FTP port (usually TCP 21) to trusted IP addresses can reduce the attack surface. Additionally, monitoring FTP server logs for unusually long NLST commands or anomalous FTP traffic patterns can help detect attempted exploitation. Employing intrusion detection/prevention systems (IDS/IPS) with signatures for buffer overflow attempts targeting IIS FTP servers may provide further protection. Finally, organizations should conduct an inventory of legacy systems and plan decommissioning or migration to reduce exposure to outdated software vulnerabilities.