Segmentation drift is the gradual weakening of network boundaries as devices, routes, exceptions, and management shortcuts are added over time. A network may start with clear trust zones, but operational changes can quietly create new paths between low-trust and high-value systems. What looked isolated on paper can become partially flat in practice.
This matters because segmentation is a core defense against lateral movement. If an attacker compromises a camera, workstation, or other exposed device, drift can give them a route to OT controllers, servers, or medical systems that were supposed to be separated. Defenders should watch for undocumented rules, temporary access that became permanent, and unexpected east-west reachability. Regular asset mapping, rule reviews, and traffic checks help keep boundaries intentional and reduce blast radius.