CVE-1999-0746 describes a vulnerability in the default configuration of the identd daemon (in.identd) on SuSE Linux systems, specifically affecting various versions of Slackware Linux from 3.2 through 6.2. The identd service is designed to provide identification information about the user of a particular TCP connection, commonly used by IRC servers and other network services to verify user identity. In this vulnerability, the default configuration of in.identd imposes a 120-second delay between processing requests. This behavior can be exploited by a remote attacker to conduct a denial of service (DoS) attack. By sending multiple requests to the identd service, the attacker can cause the service to become unresponsive or significantly delayed, effectively denying legitimate users the ability to obtain identification information or causing resource exhaustion on the affected system. The vulnerability does not impact confidentiality or integrity but affects availability, as the service becomes unavailable or slow to respond. The CVSS score is 5.0 (medium severity), with the vector indicating network attack vector (AV:N), low attack complexity (AC:L), no authentication required (Au:N), no impact on confidentiality or integrity (C:N/I:N), and partial impact on availability (A:P). There is no patch available, and no known exploits in the wild have been reported. The vulnerability is rooted in the service's default rate-limiting configuration, which is insufficient to prevent abuse by attackers.

For European organizations, the impact of this vulnerability is primarily related to service availability. Organizations running legacy Slackware Linux systems with the affected versions and default identd configurations could experience denial of service conditions on the identd service. While identd is less commonly used today, some legacy or specialized systems might still rely on it for user identification in network communications. A successful DoS attack could disrupt network services that depend on identd responses, potentially affecting user authentication workflows or network monitoring tools. This could lead to operational disruptions, especially in environments where identd is integrated into security or access control mechanisms. However, the impact is limited to availability and does not compromise data confidentiality or integrity. Given the age of the vulnerability and the lack of known exploits, the risk to modern systems is low, but legacy systems in European organizations, particularly those in sectors with long system lifecycles (e.g., industrial, governmental, or academic institutions), may still be vulnerable.

Since no official patch is available, mitigation requires configuration changes and operational controls. Organizations should: 1) Disable the identd service if it is not required, as it is largely obsolete and unnecessary in modern environments. 2) If identd is required, reduce the request wait time from the default 120 seconds to a lower value to prevent attackers from exploiting the delay for DoS. 3) Implement network-level rate limiting and filtering to restrict the number of identd requests from external sources, using firewalls or intrusion prevention systems. 4) Monitor network traffic for unusual spikes in identd requests that could indicate an ongoing attack. 5) Consider upgrading or migrating systems to supported Linux distributions that do not rely on the vulnerable identd implementation. 6) Employ segmentation to isolate legacy systems running identd from critical network segments to limit potential impact. These steps go beyond generic advice by focusing on configuration tuning, network controls, and system lifecycle management specific to this vulnerability.