Implicit trust zones are areas within a network where once access is granted, there is an assumption that all users and activities within that zone are trustworthy. This is a flaw because it does not adhere to the principle of 'least privilege' and inherently trusts the entities within the zone without continuously verifying their trustworthiness. This can lead to unauthorized access and potential breaches if a malicious actor gains access to the trusted zone and operates without restrictions. The Zero Trust model, on the other hand, never trusts and always verifies, even within the network, and is designed to operate without implicit trust zones.