CVE-1999-0053 is a vulnerability identified in FreeBSD version 6.2 that allows an attacker to cause a denial of service (DoS) condition by sending crafted TCP RST (reset) packets. The TCP RST flag is used in the TCP protocol to abruptly terminate a connection. In this vulnerability, FreeBSD's TCP/IP stack improperly handles these reset packets, enabling an attacker to disrupt active TCP connections by forcing them to close prematurely. This results in denial of service by interrupting legitimate network communications. The vulnerability does not affect confidentiality or integrity but impacts availability by terminating connections unexpectedly. The attack vector is network-based (AV:N), requires no authentication (Au:N), and has low attack complexity (AC:L). No user interaction is needed. There is no patch available for this vulnerability, and no known exploits have been reported in the wild. Given the age of the vulnerability (published in 1998) and the affected version (FreeBSD 6.2), which is itself outdated, the risk today is primarily relevant for legacy systems still running this version. The CVSS score is 5.0 (medium severity), reflecting the limited impact scope and ease of exploitation.

For European organizations, the primary impact of this vulnerability is the potential disruption of network services running on FreeBSD 6.2 systems. This could affect servers, network appliances, or embedded systems that rely on this OS version. The denial of service caused by TCP RST packets can interrupt critical communications, leading to downtime and operational disruption. While modern FreeBSD versions have addressed this issue, organizations with legacy infrastructure or specialized systems may still be vulnerable. This could impact sectors relying on high availability, such as telecommunications, finance, and critical infrastructure. However, the lack of known exploits and the obsolescence of the affected version reduce the likelihood of widespread impact. Organizations using updated FreeBSD versions or other operating systems are not affected.

Since no official patch is available for FreeBSD 6.2, organizations should prioritize upgrading to a supported and patched FreeBSD version where this vulnerability is resolved. For legacy systems that cannot be upgraded immediately, network-level mitigations can be employed, such as implementing firewall rules to filter or rate-limit suspicious TCP RST packets from untrusted sources. Intrusion detection/prevention systems (IDS/IPS) can be configured to detect abnormal TCP RST traffic patterns and alert administrators. Additionally, network segmentation can isolate vulnerable systems to reduce exposure. Regular network monitoring and incident response readiness are essential to quickly identify and mitigate any attempted exploitation. Finally, organizations should conduct an inventory of FreeBSD systems to identify and remediate any running vulnerable versions.