CVE-1999-1568 is a high-severity vulnerability affecting the NcFTPd FTP server versions prior to 2.4.1. The vulnerability arises from an off-by-one error in the handling of the PORT command, which is used by FTP clients to specify the IP address and port number for the server to connect back to for data transfer. Specifically, the server fails to properly validate or bounds-check the length of the PORT command input, allowing a remote attacker to send an overly long PORT command that triggers a buffer overflow condition by writing one byte beyond the allocated buffer boundary. This off-by-one overflow can cause the FTP server process to crash, resulting in a denial of service (DoS) condition. The vulnerability does not allow for code execution or data leakage but disrupts service availability by crashing the FTP daemon. Exploitation requires no authentication or user interaction and can be performed remotely over the network by sending a crafted PORT command to the vulnerable FTP server. Although this vulnerability was published in 1999 and affects older versions of NcFTPd, it remains relevant for legacy systems still running these outdated versions without patches or upgrades. No official patch is available for this vulnerability, so mitigation relies on upgrading to NcFTPd version 2.4.1 or later, or replacing the FTP server software with a more secure alternative. The CVSS v3.1 base score is 7.5, reflecting the high impact on availability and ease of exploitation without privileges or user interaction.

For European organizations, the primary impact of CVE-1999-1568 is service disruption due to denial of service attacks against FTP servers running vulnerable NcFTPd versions. FTP servers are often used for file transfers in enterprise environments, including for critical business operations, data exchange, and legacy system integrations. A successful DoS attack could interrupt these workflows, causing operational delays, loss of productivity, and potential financial impact. While the vulnerability does not compromise confidentiality or integrity, the availability impact can be significant if the FTP server is a critical component of the infrastructure. Organizations relying on legacy FTP servers without proper patching or upgrades are at risk. Additionally, attackers could use this DoS as a distraction or part of a multi-stage attack. Given the age of the vulnerability, modern systems are less likely to be affected, but legacy industrial control systems, research institutions, or government agencies in Europe that maintain older infrastructure may still be vulnerable. The lack of a patch means organizations must rely on mitigation strategies to reduce exposure.

1. Upgrade the NcFTPd FTP server to version 2.4.1 or later, where this off-by-one error has been fixed. If upgrading is not possible, consider replacing NcFTPd with a modern, actively maintained FTP server software that follows secure coding practices. 2. Restrict network access to FTP servers by implementing firewall rules that limit incoming connections to trusted IP addresses and networks, reducing the attack surface. 3. Employ intrusion detection/prevention systems (IDS/IPS) with signatures or heuristics to detect and block anomalous or excessively long PORT commands that could indicate exploitation attempts. 4. Monitor FTP server logs for unusual or malformed PORT commands and repeated connection attempts that may signal probing or attack activity. 5. If FTP service is not essential, consider disabling it entirely or replacing it with more secure file transfer protocols such as SFTP or FTPS, which provide encryption and improved security controls. 6. Implement network segmentation to isolate legacy systems running vulnerable FTP servers from critical production networks to contain potential impact. 7. Regularly audit and inventory network services to identify legacy FTP servers and prioritize remediation efforts.