Dear Members
Thank you for your replies.
@Anthony K. -- One of the articles that I have read mentioned that the
file gets read from the top to bottom and apply the rules accordingly. In
addition the article also explained that if there is no matching rule, the
default policy will be applied. The writer suggested that rules with the
highest chance to match should be in the beginning of the tables.
Therefore, I added them the top with the assumption that one would like to
drop non-standard packets as early as possible.
@Paul. I totally agree with you. My main objective is to master concepts
related to iptables. I never had to deal with iptables in the past,
however the landscape I find myself in, is changing and I realised the need
to develop the skill set.
@ll@xxxxxx. I was able to track down the book you have mentioned and
downloaded a copy.
Thank you once again to all. I have learned a lot from you replies.
Have an awesome week further.
Kind Regards
Leon
On Wed, Jun 29, 2016 at 5:41 PM, l@xxxxxx <l@xxxxxx> wrote:
> Hello Leon.
>
> In addition to everything else mentioned in this thread, I'd recommend you
> a great book on the topic.
> "Attack Detection and Response with iptables, psad, and fwsnort by Michael
> Rash"
> It contains a really nice and detailed guide on iptables and most common
> attacks, nmap, psad and snort.
>
> Regarding your config, I'd like to point several things:
> 1. You're not dropping packets in status 'INVALID' on top of your script,
> which is strange regarding you have 3 rules to detect other non-standard
> behavior;
> 2. Since you're blocking outgoing UDP, you should be certain that all UDP
> services are set up to use TCP instead and add corresponding rules for
> them. I'm talking about DNS queries and NTP time sync requests (as most
> common, but not limited to). These services using UDP, but you disabled it
> and haven't created outgoing rule for DNS over TCP or NTP using TCP. You
> can't do DNS queries, and it's almost always painful for any service you're
> running on your server;
> 3. Seems strange that you haven't added SMTP to the list of allowed
> outgoing connections.
>
>
>
> 29.06.2016, 13:01, "Leon Vergottini" <leonv@xxxxxxxxxxxxxxxxx>:
> > Dear Members
> >
> > I hope you are all doing well.
> >
> > I am busy teaching myself iptables and was wondering if I may get some
> > advise. The scenario is the following:
> >
> > 1. Default policy is to block all traffic
> > 2. Allow web traffic and SSH
> > 3. Allow other applications
> >
> > I have come up with the following:
> >
> > #!/bin/bash
> >
> > # RESET CURRENT RULE BASE
> > iptables -F
> > service iptables save
> >
> > # DEFAULT FIREWALL POLICY
> > iptables -P INPUT DROP
> > iptables -P FORWARD DROP
> > iptables -P OUTPUT DROP
> >
> > # ------------------------------------------------------
> > # INPUT CHAIN RULES
> > # ------------------------------------------------------
> >
> > # MOST COMMON ATTACKS
> > iptables -A INPUT -p tcp --tcp-flags ALL NONE -j DROP
> > iptables -A INPUT -p tcp ! --syn -m state --state NEW -j DROP
> > iptables -A INPUT -p tcp --tcp-flags ALL ALL -j DROP
> >
> > # LOOPBACK, ESTABLISHED & RELATED CONNECTIONS
> > iptables -A INPUT -i lo -j ACCEPT
> > iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
> >
> > # SSH
> > iptables -A INPUT -p tcp -m tcp --dport 22 -j ACCEPT
> >
> > # WEB SERVICES
> > iptables -A INPUT -p tcp -m tcp --dport 80 -j ACCEPT
> > iptables -A INPUT -p tcp -m tcp --dport 443 -j ACCEPT
> > iptables -A INPUT -p tcp -m tcp --dport 8080 -j ACCEPT
> >
> > # EMAIL
> > iptables -A INPUT -p tcp -m tcp --dport 143 -j ACCEPT
> > iptables -A INPUT -p tcp -m tcp --dport 993 -j ACCEPT
> >
> > # OTHER APPLICATIONS
> > iptables -A INPUT -p tcp -m tcp --dport XXXXX -j ACCEPT
> > iptables -A INPUT -p tcp -m tcp --dport XXXXX -j ACCEPT
> >
> > # ------------------------------------------------------
> > # OUTPUT CHAIN RULES
> > # ------------------------------------------------------
> > # UDP
> > iptables -A OUTPUT -p udp -j DROP
> >
> > # LOOPBACK, ESTABLISHED & RELATED CONNECTIONS
> > iptables -A OUTPUT -i lo -j ACCEPT
> > iptables -A OUTPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
> >
> > # SSH
> > iptables -A INPUT -p tcp -m tcp --dport 22 -j ACCEPT
> >
> > # WEB SERVICES
> > iptables -A INPUT -p tcp -m tcp --dport 80 -j ACCEPT
> > iptables -A INPUT -p tcp -m tcp --dport 443 -j ACCEPT
> > iptables -A INPUT -p tcp -m tcp --dport 8080 -j ACCEPT
> >
> > # EMAIL
> > iptables -A INPUT -p tcp -m tcp --dport 143 -j ACCEPT
> > iptables -A INPUT -p tcp -m tcp --dport 993 -j ACCEPT
> >
> > # OTHER APPLICATIONS
> > iptables -A INPUT -p tcp -m tcp --dport 11009 -j ACCEPT
> > iptables -A INPUT -p tcp -m tcp --dport 12009 -j ACCEPT
> >
> > # ------------------------------------------------------
> > # SAVE & APPLY
> > # ------------------------------------------------------
> >
> > service iptables save
> > service iptables restart
> >
> > To note:
> >
> > 1. The drop commands at the beginning of each chain is for increase
> > performance. It is my understanding that file gets read from top to
> bottom
> > and applied accordingly. Therefore, applying them in the beginning
> will
> > increase the performance by not reading through all the rules only
> to apply
> > the default policy.
> > 2. I know the above point will not really affect the performance, so
> it
> > is more of getting into a habit of structuring the rules according
> to best
> > practice, or at least establishing a pattern for myself.
> >
> > How secure is this setup? Is there any mistakes or things that I need to
> > look out for?
> >
> > Thank you in advance for your feedback.
> >
> > Kind Regards
> > Leon
> > _______________________________________________
> > CentOS mailing list
> > CentOS@xxxxxxxxxx
> > https://lists.centos.org/mailman/listinfo/centos
>
> 29.06.2016, 13:01, "Leon Vergottini" <leonv@xxxxxxxxxxxxxxxxx>:
> > Dear Members
> >
> > I hope you are all doing well.
> >
> > I am busy teaching myself iptables and was wondering if I may get some
> > advise. The scenario is the following:
> >
> > 1. Default policy is to block all traffic
> > 2. Allow web traffic and SSH
> > 3. Allow other applications
> >
> > I have come up with the following:
> >
> > #!/bin/bash
> >
> > # RESET CURRENT RULE BASE
> > iptables -F
> > service iptables save
> >
> > # DEFAULT FIREWALL POLICY
> > iptables -P INPUT DROP
> > iptables -P FORWARD DROP
> > iptables -P OUTPUT DROP
> >
> > # ------------------------------------------------------
> > # INPUT CHAIN RULES
> > # ------------------------------------------------------
> >
> > # MOST COMMON ATTACKS
> > iptables -A INPUT -p tcp --tcp-flags ALL NONE -j DROP
> > iptables -A INPUT -p tcp ! --syn -m state --state NEW -j DROP
> > iptables -A INPUT -p tcp --tcp-flags ALL ALL -j DROP
> >
> > # LOOPBACK, ESTABLISHED & RELATED CONNECTIONS
> > iptables -A INPUT -i lo -j ACCEPT
> > iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
> >
> > # SSH
> > iptables -A INPUT -p tcp -m tcp --dport 22 -j ACCEPT
> >
> > # WEB SERVICES
> > iptables -A INPUT -p tcp -m tcp --dport 80 -j ACCEPT
> > iptables -A INPUT -p tcp -m tcp --dport 443 -j ACCEPT
> > iptables -A INPUT -p tcp -m tcp --dport 8080 -j ACCEPT
> >
> > # EMAIL
> > iptables -A INPUT -p tcp -m tcp --dport 143 -j ACCEPT
> > iptables -A INPUT -p tcp -m tcp --dport 993 -j ACCEPT
> >
> > # OTHER APPLICATIONS
> > iptables -A INPUT -p tcp -m tcp --dport XXXXX -j ACCEPT
> > iptables -A INPUT -p tcp -m tcp --dport XXXXX -j ACCEPT
> >
> > # ------------------------------------------------------
> > # OUTPUT CHAIN RULES
> > # ------------------------------------------------------
> > # UDP
> > iptables -A OUTPUT -p udp -j DROP
> >
> > # LOOPBACK, ESTABLISHED & RELATED CONNECTIONS
> > iptables -A OUTPUT -i lo -j ACCEPT
> > iptables -A OUTPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
> >
> > # SSH
> > iptables -A INPUT -p tcp -m tcp --dport 22 -j ACCEPT
> >
> > # WEB SERVICES
> > iptables -A INPUT -p tcp -m tcp --dport 80 -j ACCEPT
> > iptables -A INPUT -p tcp -m tcp --dport 443 -j ACCEPT
> > iptables -A INPUT -p tcp -m tcp --dport 8080 -j ACCEPT
> >
> > # EMAIL
> > iptables -A INPUT -p tcp -m tcp --dport 143 -j ACCEPT
> > iptables -A INPUT -p tcp -m tcp --dport 993 -j ACCEPT
> >
> > # OTHER APPLICATIONS
> > iptables -A INPUT -p tcp -m tcp --dport 11009 -j ACCEPT
> > iptables -A INPUT -p tcp -m tcp --dport 12009 -j ACCEPT
> >
> > # ------------------------------------------------------
> > # SAVE & APPLY
> > # ------------------------------------------------------
> >
> > service iptables save
> > service iptables restart
> >
> > To note:
> >
> > 1. The drop commands at the beginning of each chain is for increase
> > performance. It is my understanding that file gets read from top to
> bottom
> > and applied accordingly. Therefore, applying them in the beginning
> will
> > increase the performance by not reading through all the rules only to
> apply
> > the default policy.
> > 2. I know the above point will not really affect the performance, so
> it
> > is more of getting into a habit of structuring the rules according to
> best
> > practice, or at least establishing a pattern for myself.
> >
> > How secure is this setup? Is there any mistakes or things that I need to
> > look out for?
> >
> > Thank you in advance for your feedback.
> >
> > Kind Regards
> > Leon
> > _______________________________________________
> > CentOS mailing list
> > CentOS@xxxxxxxxxx
> > https://lists.centos.org/mailman/listinfo/centos
> _______________________________________________
> CentOS mailing list
> CentOS@xxxxxxxxxx
> https://lists.centos.org/mailman/listinfo/centos
>
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