24.2. Firewall Ruleset Examples

Note

In Suricata 8 the firewall mode is experimental and subject to change.

24.2.1. HTTP

In this example a simple HTTP ruleset will be shown. It will allow HTTP to flow as long as:

• method is GET or POST

• User-Agent is "curl"

• Status code is 200.

It starts by allowing the TCP port 80 traffic.

accept:hook tcp:all any any <> any 80 (sid:10;)

The stream tracking combined with the default exception policy handling will enforce a proper TCP handshake, etc.

The HTTP rules need to accept each state:

# allow traffic before the request line is complete
accept:hook http1:request_started any any -> any any (sid:100;)
# allow GET
accept:hook http1:request_line any any -> any any ( \
        http.method; content:"GET"; sid:101;)
# or allow POST
accept:hook http1:request_line any any -> any any ( \
        http.method; content:"POST"; sid:102;)
# allow User-Agent curl
accept:hook http1:request_headers any any -> any any ( \
        http.user_agent; content:"curl"; sid:103;)
# allow the body, if any
accept:hook http1:request_body any any -> any any (sid:104;)
# allow trailers, if any
accept:hook http1:request_trailer any any -> any any (sid:105;)
# allow completion
accept:hook http1:request_complete any any -> any any (sid:106;)

# allow traffic before the response line is complete
accept:hook http1:response_started any any -> any any (sid:200;)
# allow the 200 ok stat code.
accept:hook http1:response_line any any -> any any ( \
        http.stat_code; content:"200"; sid:201;)
# allow all other states
accept:hook http1:response_headers any any -> any any (sid:202;)
accept:hook http1:response_body any any -> any any (sid:203;)
accept:hook http1:response_trailer any any -> any any (sid:204;)
accept:hook http1:response_complete any any -> any any (sid:205;)

Each state needs an accept rule. Each state is evaluated at least once.

24.2.2. TLS SNI with complex TCP rules

In this example the packet_filter rules will be more opinionated about the traffic:

# allow 3-way handshake
accept:hook tcp:all $HOME_NET any -> $EXTERNAL_NET 443 (flags:S; \
        flow:not_established; flowbits:set,syn; sid:1;)
accept:hook tcp:all $EXTERNAL_NET 443 -> $HOME_NET any (flags:SA; \
        flow:not_established; flowbits:isset,syn; flowbits:set,synack; sid:2;)
accept:hook tcp:all $HOME_NET any -> $EXTERNAL_NET 443 (flags:A; \
        flow:not_established; flowbits:isset,synack;             \
        flowbits:unset,syn; flowbits:unset,synack; sid:3;)
# allow established
accept:hook tcp:all $HOME_NET any <> $EXTERNAL_NET 443 (flow:established; sid:4;)

Then on the TLS level this will be a TLS SNI firewall.

Again all the states need to be accepted. Only in the client_hello_done state will there be additional constraints:

accept:hook tls:client_in_progress $HOME_NET any -> $EXTERNAL_NET any (sid:100;)
# allow the good sites
accept:hook tls:client_hello_done $HOME_NET any -> $EXTERNAL_NET any (tls.sni; \
        pcre:"/^(suricata.io|oisf.net)$/; sid:101;)
accept:hook tls:client_cert_done $HOME_NET any -> $EXTERNAL_NET any (sid:102;)
accept:hook tls:client_handshake_done $HOME_NET any -> $EXTERNAL_NET any (sid:103;)
accept:hook tls:client_finished $HOME_NET any -> $EXTERNAL_NET any (sid:104;)

accept:hook tls:server_in_progress $EXTERNAL_NET any -> $HOME_NET any (sid:200;)
accept:hook tls:server_hello $EXTERNAL_NET any -> $HOME_NET any (sid:201;)
accept:hook tls:server_cert_done $EXTERNAL_NET any -> $HOME_NET any (sid:202;)
accept:hook tls:server_hello_done $EXTERNAL_NET any -> $HOME_NET any (sid:203;)
accept:hook tls:server_handshake_done $EXTERNAL_NET any -> $HOME_NET any (sid:204;)
accept:hook tls:server_finished $EXTERNAL_NET any -> $HOME_NET any (sid:205;)