CVE-1999-0349 is a high-severity buffer overflow vulnerability found in Microsoft Internet Information Server (IIS) versions 3.0 and 4.0, specifically within the FTP service's LIST (ls) command. The vulnerability arises due to improper handling of input data in the FTP LIST command, which allows a remote attacker to send specially crafted requests that overflow a buffer in the server's memory. This overflow can lead to denial of service (DoS) by crashing the FTP service, and in some cases, it can be exploited to execute arbitrary code remotely. The vulnerability does not require authentication and can be triggered over the network, making it accessible to any attacker with network access to the FTP service. The CVSS v2 score of 7.5 reflects the high impact on confidentiality, integrity, and availability, combined with low attack complexity and no authentication requirement. Although this vulnerability dates back to 1999 and affects legacy IIS versions, unpatched systems remain at risk. Microsoft has released patches to address this issue, and the vulnerability is classified under CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer). No known exploits in the wild have been reported, but the potential for remote code execution elevates the threat level significantly.

For European organizations, the impact of this vulnerability can be substantial if legacy IIS 3.0 or 4.0 servers are still in use, particularly in environments where FTP services are exposed to external networks. Exploitation could lead to service outages affecting business operations due to denial of service, and in worst cases, attackers could gain control over affected servers, leading to data breaches, lateral movement within networks, or deployment of malware. Given the age of the vulnerability, it is less likely to affect modern infrastructures; however, organizations with legacy systems or those in industrial, governmental, or critical infrastructure sectors that rely on older software versions could face significant operational and reputational damage. Additionally, compliance with European data protection regulations (e.g., GDPR) could be jeopardized if personal or sensitive data is compromised as a result of exploitation.

European organizations should first identify any IIS 3.0 or 4.0 servers running FTP services within their networks. Immediate mitigation involves applying the official Microsoft patches referenced in the security bulletin MS99-003. If patching is not feasible due to legacy system constraints, organizations should consider disabling the FTP service or restricting access to it via network segmentation and firewall rules, limiting exposure to trusted IP addresses only. Employing intrusion detection/prevention systems (IDS/IPS) with signatures for buffer overflow attempts targeting FTP services can help detect and block exploitation attempts. Additionally, organizations should plan for upgrading legacy IIS servers to supported versions or migrating to modern, secure FTP solutions. Regular vulnerability scanning and penetration testing should be conducted to ensure no vulnerable instances remain. Finally, monitoring logs for unusual FTP activity can provide early warning signs of attempted exploitation.