CVE-1999-1346 is a vulnerability found in the Pluggable Authentication Module (PAM) configuration for the rlogin service on Red Hat Linux 6.1 and earlier versions. The issue arises because the PAM configuration file contains a less restrictive rule placed before a more restrictive one, effectively allowing users to bypass intended access controls. Specifically, even if the system administrator has disabled rlogin access by creating the /etc/nologin file—a standard method to prevent user logins during maintenance or other administrative tasks—the flawed PAM configuration permits users to still access the host via rlogin. This vulnerability stems from the order and logic of PAM rules, where the permissive rule takes precedence, undermining the security controls. The vulnerability has a CVSS score of 7.5 (high severity), with a vector indicating 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). Although this vulnerability dates back to 1999 and affects legacy systems, it represents a critical misconfiguration that could allow unauthorized remote access, potentially leading to privilege escalation, data exposure, or system compromise. No patches are available, and there are no known exploits in the wild, likely due to the age and obsolescence of the affected systems.

For European organizations, the impact of this vulnerability is primarily relevant if legacy Red Hat Linux 6.1 or earlier systems are still in use, which is uncommon in modern IT environments. However, in industrial control systems, embedded devices, or legacy infrastructure that has not been updated, this vulnerability could allow unauthorized remote access via rlogin, bypassing intended login restrictions. This unauthorized access could lead to data breaches, unauthorized system changes, or disruption of services. Given the vulnerability allows remote unauthenticated access, attackers could exploit it to compromise confidentiality, integrity, and availability of affected systems. The impact is heightened in environments where rlogin is used for remote management without additional security layers. For European organizations, especially those in critical infrastructure sectors or with legacy systems in operation, this vulnerability could pose a risk if not mitigated. However, the overall risk is low for most modern enterprises due to the obsolescence of the affected software version and the decline in rlogin usage in favor of more secure protocols like SSH.

Since no official patch is available for this vulnerability, organizations should take the following specific actions: 1) Immediately discontinue the use of rlogin service on all systems, especially legacy Red Hat Linux 6.1 and earlier versions. 2) Replace rlogin with secure alternatives such as SSH, which provide encrypted and more robust authentication mechanisms. 3) Audit all systems to identify any legacy Red Hat Linux installations and plan for their upgrade or decommissioning. 4) If legacy systems must remain operational, manually review and correct PAM configuration files to ensure that restrictive rules precede permissive ones, effectively enforcing login restrictions. 5) Implement network-level controls such as firewall rules to block rlogin (TCP port 513) traffic from untrusted networks. 6) Monitor logs for any unauthorized rlogin attempts and unusual access patterns. 7) Educate system administrators about the risks of legacy authentication services and encourage migration to supported, secure platforms.