How to test if SYN and FIN are both dropped at the same time in hping3?

Posted by snow on Server Fault See other posts from Server Fault or by snow
Published on 2011-02-04T04:58:45Z Indexed on 2011/02/04 7:27 UTC
Read the original article Hit count: 427

Filed under:

iptables

One of the rules to prevent unexpected attack is to prevent SYN & FIN being used together.

SYN and FIN are both set

$IPT -A INPUT -p tcp --tcp-flags SYN,FIN SYN,FIN -j DROP

How do I use hping to test if this iptable rule works? hping3 192.168.7.0 --keep -S -F??? Is this complete?

When just type iptables -L, it shows:

Chain INPUT (policy DROP) target prot opt source destination
ACCEPT all -- anywhere anywhere
DROP tcp -- anywhere anywhere tcp flags:FIN,SYN/FIN,SYN

WHY do I need to put the "SYN,FIN" twice before drop? Is it because one for source and one for destination?

Related posts about iptables

Sometimes this script fails to update the iptables

as seen on Server Fault - Search for 'Server Fault'
It does not happen often, but sometimes after running the below script, checking the iptables with service iptables status shows that they weren't updated and the script doesn't output any error. The iptables is structured as look-up tree (long repeated sections snipped): #!/bin/sh iptables -t… >>> More
My current iptable configuration doesn't work [on hold]

as seen on Server Fault - Search for 'Server Fault'
sudo chkconfig iptables off /etc/init.d/iptables on ### Clear/flush iptables sudo iptables -F sudo iptables -P INPUT ACCEPT sudo iptables -P OUTPUT ACCEPT sudo iptables -P FORWARD ACCEPT ### Allow SSH iptables -A INPUT -i eth0 -p tcp --dport 22 -m state --state NEW,ESTABLISHED -j ACCEPT iptables… >>> More
L2TP iptables port forward

as seen on Server Fault - Search for 'Server Fault'
Hi all, I'm setting up port forwarding for an L2TP VPN connection to the local Windows 2003 VPN server. The router is a simpel Debian machine with iptables. The VPN server works perfect. But I cannot log in from the WAN. I'm missing something. The VPN server is using a pre-shared key (L2TP) and… >>> More
iptables -P FORWARD DROP makes port forwarding slow

as seen on Server Fault - Search for 'Server Fault'
I have three computers, linked like this: box1 (ubuntu) box2 router & gateway (debian) box3 (opensuse) [10.0.1.1] ---- [10.0.1.18,10.0.2.18,10.0.3.18] ---- [10.0.3.15] | box4, www [10.0.2.1] Among other… >>> More
IPtables AWS EC2 NAT/Reverse NAT - For Reverse Proxy style setup but with IPtables

as seen on Server Fault - Search for 'Server Fault'
I was thinking initially needing to do a reverse proxy or something so I could get some SSL/TLS traffic look like it is being terminated at a server and IP address in the AWS cloud, and then that traffic is forwarded onto our actual web servers that aren't in the cloud... I've not done much iptables… >>> More

Developer IT