CVE-1999-0763 in NetBSD
Summary
by MITRE
NetBSD on a multi-homed host allows ARP packets on one network to modify ARP entries on another connected network.
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Analysis
by VulDB Data Team • 04/19/2026
The vulnerability described in CVE-1999-0763 represents a significant network security flaw in the NetBSD operating system that affects multi-homed hosts. This issue arises from improper handling of Address Resolution Protocol (ARP) packets across multiple network interfaces, creating a scenario where malicious actors can manipulate ARP tables on networks they should not have direct access to. The vulnerability specifically impacts systems configured with multiple network interfaces connected to different networks, where each interface maintains its own ARP cache. When an ARP packet is received on one interface, the system should ideally validate that the packet originates from the correct network segment before updating its ARP table for that specific interface.
The technical flaw stems from the lack of proper network segmentation validation within the ARP processing mechanism. In a properly secured multi-homed system, ARP packets should be filtered based on their source network address and the interface through which they were received. However, NetBSD versions affected by this vulnerability fail to implement such validation, allowing ARP requests and replies from one network segment to inadvertently update ARP entries on interfaces connected to different networks. This behavior creates an attack vector where an attacker on one network segment can poison the ARP cache of another network segment, potentially enabling man-in-the-middle attacks, traffic interception, or network disruption. The vulnerability operates at the network layer and specifically impacts the ARP protocol implementation, which is fundamental to IP network communication.
The operational impact of this vulnerability is substantial for multi-homed network environments where security isolation between network segments is critical. An attacker positioned on a single network segment can leverage this flaw to gain unauthorized access to other network segments by manipulating ARP tables, effectively breaking network segmentation policies. This capability allows for various malicious activities including network reconnaissance, traffic interception, and potential data exfiltration. The vulnerability particularly affects enterprise environments where multi-homed servers are commonly deployed to provide network services across multiple network segments, making it a serious concern for organizations relying on proper network isolation. The impact extends beyond simple network disruption to potentially enable more sophisticated attacks that exploit the compromised ARP tables for further lateral movement within the network infrastructure.
This vulnerability aligns with CWE-284 Access Control Issues and relates to the broader category of network protocol implementation flaws that violate the principle of least privilege. From an ATT&CK framework perspective, this vulnerability maps to techniques such as ARP cache poisoning and network sniffing, enabling adversaries to establish persistent access to network segments they should not be able to reach. The mitigation strategies for this vulnerability include implementing proper ARP validation mechanisms, configuring network segmentation controls, and ensuring that ARP packets are properly filtered based on their source network addresses. System administrators should also consider implementing ARP monitoring tools to detect anomalous ARP activity and deploy network access control lists to prevent ARP packets from crossing network boundaries. Additionally, upgrading to patched versions of NetBSD that properly implement ARP validation across multiple network interfaces represents the most effective long-term solution to prevent exploitation of this vulnerability.