da terminale

vi /etc/apt/sources.list

cancella tutto e inserisci queste due linee

deb http://kali.mirror.garr.it/mirrors/kali/ kali-rolling main contrib non-free
deb-src http://kali.mirror.garr.it/mirrors/kali/ kali-rolling main contrib non-free

salva ed esci

poi

apt-get update
apt-get upgrade
apt-get dist-upgrade
reboot