The present disclosure relates to a pre-5th-Generation (5G) or 5G communication system to be provided for supporting higher data rates Beyond 4th-Generation (4G) communication system such as Long Term Evolution. Methods and systems for mitigating Denial of Service (DOS) attacks in wireless networks, by performing admission control by verifying a User Equipment's (UE's) registration request via a Closed Access Group (CAG) cell without performing a primary authentication are provided. Embodiments herein disclose methods and system for verifying permissions of the UE to access a CAG cell based on the UE's Subscription identifier, before performing the primary authentication. The method for mitigating DOS attacks in wireless networks includes requesting a public land mobile network for accessing a non-public network (NPN) through a CAG cell, verifying the permissions of a UE to access the requested NPN through the CAG cell, and performing a primary authentication.