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linuxlinux-kerneliptables

iptable rule to drop packet with a specific substring in payload

I am trying to write rules to drop any packet, irrespective if it is outgoing, incoming or being forwarded, which has a specific sub string in the TCP or UDP payload.

How am I suppose to do that?

Solution

  • You'd need a kernel compiled with Netfilter "String match support" enabled.

    Then you can 

    iptables -A INPUT -m string --algo bm --string "test" -j DROP
iptables -A OUTPUT -m string --algo bm --string "test" -j DROP
iptables -A FORWARD -m string --algo bm --string "test" -j DROP

    Check the result wth

    iptables -L