I thought Linux was SAFER than Windows?

amateur_intermediate · 01-09-2022, 10:21 AM

Hello, everyone!

I have a small web-server and wanted to tighten up security by adding some recommended iptable rules online, but this looks dubious.

My question is about the -limit module in iptables in combination with the LOG target.

I understand the drop rules below, but it seems to me that -m limit portions are screwing up the rules.

Code:

$IPT -t mangle -A PREROUTING -p tcp --tcp-flags FIN,RST FIN,RST -m limit --limit 25/min -j LOG --log-prefix "BLOCKING-TCP"
$IPT -t mangle -A PREROUTING -p tcp --tcp-flags FIN,RST FIN,RST -j DROP

$IPT -t mangle -A PREROUTING -p tcp -m conntrack --ctstate NEW -m tcpmss ! --mss 536:65535 -m limit --limit 25/min -j LOG --log-prefix "BLOCKING-TCP"
$IPT -t mangle -A PREROUTING -p tcp -m conntrack --ctstate NEW -m tcpmss ! --mss 536:65535 -j DROP

$IPT -t mangle -A PREROUTING -p tcp --tcp-flags ALL FIN,PSH,URG -m limit --limit 25/min -j LOG --log-prefix "BLOCKING-TCP"
$IPT -t mangle -A PREROUTING -p tcp --tcp-flags ALL FIN,PSH,URG -j DROP

$IPT -t mangle -A PREROUTING -p tcp ! --syn -m state --state NEW -m limit --limit 25/min -j LOG --log-prefix "BLOCKING-TCP"
$IPT -t mangle -A PREROUTING -p tcp ! --syn -m state --state NEW -j DROP

$IPT -t mangle -A PREROUTING -p tcp --tcp-flags ALL ALL -m limit --limit 25/min -j LOG --log-prefix "BLOCKING-TCP"
$IPT -t mangle -A PREROUTING -p tcp --tcp-flags ALL ALL -j DROP

Reading the manpage, the principle of only matching the rule n times and thus only logging it n times is fine, but these rules include special instructions where this cannot work I believe and it will actually interfere with each DROP rule below.

For example this makes perfect sense:
(Logging incoming tcp packets on port 80 / 25 packets per minute, i.e 25 log entries per minute)

Code:

$IPT -A INPUT -p tcp -m tcp --dport 80 -m limit --limit 25/min -j LOG --log-prefix "BLOCKING-TCP"

But this just seems really wrong and I can't make any sense of it:

Code:

$IPT -t mangle -A PREROUTING -p tcp -m conntrack --ctstate NEW -m tcpmss ! --mss 536:65535 -m limit --limit 25/min -j LOG --log-prefix "BLOCKING-TCP"

rtmistler · 01-09-2022, 12:21 PM

Please post your thread in only one forum. Posting a single thread in the most relevant forum will make it easier for members to help you and will keep the discussion in one place. This thread is being closed because it is a duplicate.

This matches your update here from this other thread, please continue in that original thread to avoid confusion.