An adjacent-network attacker is a threat actor who is not necessarily on the public internet but is already connected to the same local network, or is close enough to observe or interfere with it. In practice, this can mean a device on a home Wi-Fi network, a guest network, a nearby rogue access point, or a compromised machine inside the same office segment.
This attacker model matters because many bugs are only reachable from inside the trust boundary. In router and web-management flaws, an adjacent attacker may be able to send crafted requests, intercept unencrypted login traffic, or trigger service crashes that remote outsiders cannot reach. Defenders reduce this risk by segmenting networks, isolating guests and IoT devices, using encrypted management sessions, disabling unnecessary features, and treating local access as hostile rather than safe.