Para referência futura ou para qualquer pessoa que veja esta página, aqui está o script finalizado:
#!/bin/sh
PATH=/usr/sbin:/sbin:/bin:/usr/bin
#
# delete all existing rules.
#
iptables -F
iptables -t nat -F
iptables -t mangle -F
iptables -X
# Always accept loopback traffic
iptables -A INPUT -i lo -j ACCEPT
# Allow established connections, and those not coming from the outside
iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
iptables -A INPUT -m state --state NEW ! -i wlan0 -j ACCEPT
iptables -A FORWARD -i wlan0 -o eth0 -m state --state ESTABLISHED,RELATED -j ACCEPT
# Allow outgoing connections from the LAN side.
iptables -A FORWARD -i eth0 -o wlan0 -j ACCEPT
# Masquerade.
iptables -t nat -A POSTROUTING -o wlan0 -j MASQUERADE
# Don't forward from the outside to the inside.
iptables -A FORWARD -i wlan0 -o wlan0 -j REJECT
#Port Forward Unifed remote
iptables -A INPUT -p tcp --dport 9512 -j ACCEPT -i wlan0
iptables -t nat -A PREROUTING -p tcp --dport 9512 -j DNAT --to-destination 10.1.1.12:9512
iptables -t nat -A POSTROUTING -d 10.1.1.12 -p tcp --dport 9512 -j SNAT --to-source 10.1.1.1
# Drop outside traffic except ssh
iptables -A INPUT -p tcp --dport ssh -j ACCEPT -i wlan0
iptables -A INPUT -j DROP -p tcp -i wlan0
# Enable routing.
echo 1 > /proc/sys/net/ipv4/ip_forward