[BrutalGoerge]

for linux, just use this iptables rule.
iptables -A INPUT -p udp --dport 27015 -m length --length 28 -j DROP

--dport <whatever ports you're using for your servers>

looking at your sig.. these 2 should work
iptables -A INPUT -p udp --dport 27015 -m length --length 28 -j DROP
iptables -A INPUT -p udp --dport 27016 -m length --length 28 -j DROP