Wireless Local Area Network (WLAN) at the Faculty of Engineering and Science, University of Muhammadiyah Purwokerto, besides making it easier for students, employees, and lecturers to access data and access the internet, can be misused by irresponsible people. The purpose of this study is to analyze network security, to find out whether the wireless Faculty of Engineering and Science has network security holes. In analyzing the WLAN network, the Penetration Testing method is carried out where the attack on the network is simulated, one of the operating systems that have the right specifications in this case is Kali Linux. The results of this study indicate that WLAN in the Faculty of Engineering and Science still has security holes to be exploited. This is evidenced by the results of research conducted on man-in-the-middle attacks when accessing websites with the HTTP protocol username and password can be captured in the ettercap application, whereas when accessing websites with the HTTPS protocol the username and password cannot be captured.