full-disclosure - reduction of brute force log

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Date: Tue Feb 28 18:03:38 2006
From: j.schipper at math.uu.nl (Joachim Schipper)
Subject: reduction of brute force log

On Tue, Feb 28, 2006 at 10:52:27AM -0600, Bob Radvanovsky wrote:
> I am going to test these rules out -- this looks REALLy good!
> But...I've got just ONE question: why on Earth would you permit
> ICMP???

(Outgoing) echo requests and port-unreachable responses (to UDP
packets), just to name a couple.

Source quench and redirect are both powerful, but also more than a
little dangerous to allow.

> And what significances are ports 50, 51, 1599, 1600 and 1601?  443 and 80 are HTTP-S and HTTP (respectively), 123 is NTP -- I realize that, but what are these others ports used for?

We are talking about IP *protocols* 50 and 51, which are ESP and AH -
the IPsec protocols.

The 1599-1601 ports are used to open/close the ssh port, as explained in
the article linked.

This firewall configuration should work as advertised. Of course,
restricting logins to public key authentication should work, and has the
added advantage that one does not try to login from yet another
keylogger-infected Windows box.

		Joachim

> -r
> 
> *filter
> :INPUT ACCEPT [0:0]
> :FORWARD ACCEPT [0:0]
> :OUTPUT ACCEPT [0:0]
> :RH-Firewall-1-INPUT - [0:0]
> -A INPUT -j RH-Firewall-1-INPUT
> -A FORWARD -j RH-Firewall-1-INPUT
> -A RH-Firewall-1-INPUT -i lo -j ACCEPT
> -A RH-Firewall-1-INPUT -s 10.0.0.0/24 -j ACCEPT
> -A RH-Firewall-1-INPUT -p icmp --icmp-type any -j ACCEPT
> -A RH-Firewall-1-INPUT -p 50 -j ACCEPT
> -A RH-Firewall-1-INPUT -p 51 -j ACCEPT
> -A RH-Firewall-1-INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
> -A RH-Firewall-1-INPUT -m state --state NEW -m tcp -p tcp --dport 22 -m recent --rcheck --name SSH -j ACCEPT
> -A RH-Firewall-1-INPUT -m state --state NEW -m tcp -p tcp --dport 80 -j ACCEPT
> -A RH-Firewall-1-INPUT -m state --state NEW -m udp -p udp --dport 123 -j ACCEPT
> -A RH-Firewall-1-INPUT -m state --state NEW -m tcp -p tcp --dport 443 -j ACCEPT
> -A RH-Firewall-1-INPUT -m state --state NEW -m tcp -p tcp --dport 1599 -m recent --name SSH --remove -j DROP
> -A RH-Firewall-1-INPUT -m state --state NEW -m tcp -p tcp --dport 1600 -m recent --name SSH --set -j DROP
> -A RH-Firewall-1-INPUT -m state --state NEW -m tcp -p tcp --dport 1601 -m recent --name SSH --remove -j DROP
> -A RH-Firewall-1-INPUT -j REJECT --reject-with icmp-host-prohibited
> COMMIT
> 
> 
> ----- Original Message -----
> From: Matthijs van Otterdijk [mailto:thotter@...il.com]
> To: full-disclosure@...ts.grok.org.uk
> Subject: Re: [Full-disclosure] reduction of brute force login attempts via SSH	through iptables --hashlimit
> 
> 
> > I haven't tried this myself, and I don't know if it is already suggested,
> > but this should stop all the pesky scriptkiddies from filling up your logs.
> > Might prove to be a better solution, who knows:
> > http://aplawrence.com/Security/sshloginattack.html
> > 
> > Matthijs