Adjacent access means an attacker must be close to the target or connected to the same local network, bus, or radio domain. It is not remote internet access. In security models, this usually lowers the attacker’s reach but raises the importance of physical security, network segmentation, and trusted maintenance paths.
This term matters in industrial and building automation because many devices are exposed through local buses and on-site service ports. If an attacker can plug into the same wiring or reach the same internal segment, they may tamper with configuration, intercept traffic, or abuse weak firmware-update workflows. Defenses focus on limiting local entry, authenticating devices and updates, and using secure variants of protocols so that proximity alone is not enough to gain control.