An uninitialized use refers to a common coding mistake where programmers directly use variables on the stack or the heap before they are initialized. Uninitialized uses, although simple, can lead to severe security consequences. In this paper, we will share our experience in gaining arbitrary kernel code execution in the latest macOS Sierra by exploiting two uninitialized use vulnerabilities for Pwnfest 2016. Specifically, we first analyze the attack surface of the XNU kernel and mitigation techniques, and then study common types of uninitialized uses and potential threats. Then we elaborate on the vulnerabilities and exploitation techniques. Lastly, we summarize the whole exploitation and discuss the reliability of the exploitation.