CVE-1999-0764 is a vulnerability in NetBSD version 1.3 where the operating system allows Address Resolution Protocol (ARP) packets to overwrite static ARP entries. ARP is a protocol used to map IP addresses to MAC addresses on a local network. Static ARP entries are manually configured mappings intended to be immutable to prevent spoofing or unauthorized changes. However, in this vulnerability, NetBSD does not properly protect these static entries, allowing malicious ARP packets to overwrite them. This can lead to ARP spoofing or poisoning attacks, where an attacker sends forged ARP messages onto the network to associate their MAC address with the IP address of another host, such as a gateway or another critical system. The vulnerability requires no authentication and can be exploited remotely over the network (AV:N), with low attack complexity (AC:L). The impact includes partial loss of integrity (I:P) and availability (A:P) but no confidentiality loss (C:N). Exploiting this vulnerability can disrupt network communications, redirect traffic, or facilitate man-in-the-middle attacks. Although no patches are available and no known exploits are reported in the wild, the vulnerability remains a concern for systems still running this legacy version of NetBSD.

For European organizations, this vulnerability poses risks primarily in environments where legacy NetBSD 1.3 systems are still operational, such as in embedded systems, research, or specialized network appliances. Successful exploitation could allow attackers to manipulate network traffic, leading to denial of service or interception of sensitive communications within local networks. This could disrupt business operations, especially in sectors relying on stable internal networking like manufacturing, utilities, or telecommunications. While the vulnerability does not directly expose confidential data, the ability to alter network traffic integrity and availability can indirectly compromise security and operational continuity. Given the age of the vulnerability and the lack of patches, organizations still using affected versions face increased risk due to unmitigated exposure.

Specific mitigation steps include: 1) Upgrading from NetBSD 1.3 to a supported, patched version of NetBSD or an alternative modern operating system that properly enforces static ARP entry protection. 2) Implementing network-level controls such as Dynamic ARP Inspection (DAI) on switches to validate ARP packets and prevent spoofing. 3) Using static ARP entries sparingly and only on trusted devices, combined with network segmentation to limit exposure. 4) Employing intrusion detection systems (IDS) capable of detecting ARP spoofing attempts. 5) Monitoring network traffic for unusual ARP activity and anomalies. 6) Where upgrading is not immediately feasible, restricting network access to vulnerable hosts and isolating them from critical infrastructure can reduce risk.