Para corrigir os problemas de cabeçalho e kernel, adicionei deb http://mirror.nus.edu.sg/kali/kali kali-rolling main non-free contrib
à minha lista de fontes. Porque eu estava instalando o pacote deb do VB, eu estava conseguindo:
RTR3InitEx failed with rc=-1912 (rc=-1912)
The VirtualBox kernel modules do not match this version of VirtualBox. The installation of VirtualBox was apparently not successful. Executing
'/sbin/vboxconfig'
may correct this. Make sure that you do not mix the OSE version and the PUEL version of VirtualBox.
where: supR3HardenedMainInitRuntime what: 4 VERR_VM_DRIVER_VERSION_MISMATCH (-1912) - The installed support driver doesn't match the version of the user.
Não tenho certeza do que estava causando esse problema, mas corrigi-lo limpando a instalação deb e reinstalando o VB com apt-get install virtualbox
.