4 steps to fix: Unable to locate package virtualbox-guest-x11 (Kali Linux 2018)

You won’t believe how quickly this Kali Linux issue can be fixed. You just need to add one line to your /etc/apt/sources.list file.

You need to add this line to /etc/apt/sources.list:

deb http://http.kali.org/kali kali-rolling main contrib non-free