CVE-1999-0651 identifies the presence of the rsh (remote shell) and rlogin (remote login) services running on a system. These services were designed to allow users to execute commands and log into remote systems over a network without requiring strong authentication or encryption. Both rsh and rlogin rely on trust relationships and transmit data, including credentials, in plaintext, making them inherently insecure by modern standards. The vulnerability itself is the continued use or exposure of these services, which can be exploited by attackers to intercept sensitive information, perform unauthorized remote command execution, and potentially gain full control over affected systems. The CVSS score of 7.5 (high) reflects the network attack vector (AV:N), low attack complexity (AC:L), no authentication required (Au:N), and impacts on confidentiality, integrity, and availability (C:P/I:P/A:P). Since these services do not require authentication and transmit data unencrypted, attackers can easily perform man-in-the-middle attacks or spoof trusted hosts to gain unauthorized access. Although no patches exist because this is a design flaw and deprecated service, the presence of these services on modern networks represents a significant security risk.

For European organizations, the presence of rsh/rlogin services can lead to severe security breaches. Attackers can intercept sensitive credentials and data transmitted over the network, leading to unauthorized access to critical systems. This can compromise confidentiality of sensitive business information, integrity of system configurations and data, and availability of services if attackers execute malicious commands or disrupt operations. European organizations in sectors such as finance, government, healthcare, and critical infrastructure are particularly at risk due to the sensitive nature of their data and regulatory requirements like GDPR. The use of these legacy services can also lead to non-compliance with security standards and audits, resulting in legal and reputational damage. Furthermore, the ease of exploitation means that even less sophisticated attackers can leverage this vulnerability to gain footholds in networks, potentially leading to lateral movement and broader compromise.

Given that no patches exist for the inherent insecurity of rsh/rlogin, the primary mitigation is to completely disable these services on all systems. Organizations should audit their networks to identify any hosts running rsh or rlogin daemons and remove or disable them immediately. Replace these services with secure alternatives such as SSH (Secure Shell), which provides encrypted communication and strong authentication mechanisms. Network segmentation and firewall rules should be implemented to block traffic on ports associated with rsh (TCP 514) and rlogin (TCP 513). Additionally, organizations should conduct regular vulnerability scans and penetration tests to ensure no legacy services remain active. Employee training and awareness programs should emphasize the risks of legacy protocols and the importance of using secure remote access methods. Monitoring network traffic for unusual activity related to these ports can also help detect attempts to exploit these services.