Dev tunnels are legitimate developer tools that relay traffic from a remote endpoint to a service running on a local machine or private network. They are commonly used to expose a web app, API, or test server without changing firewall rules or opening a permanent inbound port. The tunnel creates an outward connection to a relay service, then forwards requests back to the target service.
In cyber security, dev tunnels matter because their normal, trusted behavior can be abused for stealthy access. An attacker with stolen credentials or a compromised host may use a tunnel to make remote desktop, admin panels, or other internal services look like ordinary developer traffic. This can bypass simple perimeter scanning and hide the real source of access. Defenders should inventory approved tunneling tools, log tunnel creation and destination changes, and alert on unusual account-to-service pairings or unexpected remote-access patterns.