Get the Whitepaper called Security Issues in Android Custom ROMs. This paper keeps a special focus on custom ROMs by checking for security misconfigurations that can lead to device compromise.
You can download it from the following link: https://packetstormsecurity.com/files/download/105895/android-custom-rom.pdf
Source: https://packetstormsecurity.com/files/105895/Security-Issues-In-Android-Custom-ROMs.html