Digital dependency is reliance on external systems or services that an organization does not fully control, such as cloud platforms, identity providers, managed IT, software vendors, and hosted business tools. These dependencies become part of the organization’s real attack surface because their availability, security, and configuration can affect internal operations, data access, and incident response.
It matters in cyber security because a failure or compromise outside the perimeter can still cause breach, outage, or disruption inside the business. Attackers may target a supplier, update channel, or shared service to reach many downstream victims, while defenders use dependency mapping, supplier assurance, segmentation, continuity planning, and incident playbooks to reduce the blast radius. Strong security now requires knowing which external services are critical and what happens if they fail.