How to block traffic in LINUX by its content?

Question

firewall

Good day to all! Actually there is a socks5 proxy, you need to block traffic going through it to the 25th port. How can I do that? As I understand it, you need to somehow watch the contents of the traffic itself and block it by content somehow.

Answer 1

You need to create rules in iptables for incoming connection to port 25 with proxy ip.
I don't remember exactly the syntax, but it seems the rule should be:
iptables -A INPUT -s 666.13.666.13/25 -j DROP

Answer 2

By means of socks
3proxy itself: HowTo (English)
allow userlist sourcelist targetlist targetportlist
deny userlist sourcelist targetlist targetportlist
flush

Answer 3

depending on what is meant by content. if you know exactly the regular expression of the text you want to drop, then iptables has modules of the "string" type, with which you can find the necessary data and drop it.