[arm-allstar] Firewall thoughts ---was:Trouble with Supermon
Mark Grigsby
ka7fha at gmail.com
Sat May 19 14:48:48 EST 2018
I am new to allstar hamvoip and the list. I would like to say thank you
for all the hard work others do. In regard to the iptables / netfilter
rule above, I think there might be a little confusion about the meaning of
the rule.
""iptables -A INPUT -p tcp -m tcp --dport 222 -m state --state NEW -m
recent --update --seconds 60 --hitcount 4 --name DEFAULT --rsource -j DROP""
In this rule you have to make an attempt to connect to the ssh server 4
times in 60 seconds, the 5th connection withing 60 seconds will be denied.
Many ssh servers will allow several attempts at passwords and the hamvoip
server allows up to 6 failures before it disconnects you. As long as you
don't exceed 4 connections in 60 seconds (one attempt every 20 seconds)
this rule will never activate, and if you pause for 60 seconds it will
automatically clear the offending address from the firewall. this means
that you could try 24 combinations in 60 seconds then pause for 60 seconds
and try all over again.
I use a slightly different version that I will explain below.
iptables -A INPUT -p tcp --dport 22 ! -s 192.168.12.0/27 -m conntrack
--ctstate NEW -m recent --set --name SSH
iptables -A INPUT -p tcp --dport 22 ! -s 192.168.12.0/27 -m conntrack
--ctstate NEW -m recent --update --seconds 600 --hitcount 4 --rttl --name
SSH -j DROP
The difference in this command is that any connections from my personal
virtual host network (192.168.12.0/27) is ignored, and I can try as many
times as I like with no fear of getting locked out. The second part is
that you only have to try 4 times in 10 minutes before you get locked out.
I have also set my ssh server to only allow 3 attempts per connection and
additionally I force the use of ssh keys and never allow passwords to be
entered interactively.
In my "day-Job" I also record the IP address of repeated failed logins and
generate a list of addresses that I import to the firewall to deny them
before they get a chance.
I hope this helps someone, and I would be happy to discuss this and help
others that may not be comfortable at the command line.
On Thu, May 17, 2018 at 3:12 PM, "Charles Powell via arm-allstar" <
arm-allstar at hamvoip.org> wrote:
> I have tacked my last rule as an addition to Doug’s (WA3DSP)’s iptables
> entry for Supermon. One note - since I have dynamic DNS at all points for
> my nodes, I do NOT run this in a cron tab. I use the name instead of IP in
> Doug’s script. That way I only run the script at boot from /etc/rc.local
> and does not get flushed out every 10 minutes or whatever the interval
> was. So here is my addition to the end of the file:
>
>
> iptables -A INPUT -p tcp -m tcp --dport 222 -m state --state NEW -m
> recent --update --seconds 60 --hitcount 4 --name DEFAULT --rsource -j DROP
>
> # Use this statement at the Linux prompt to view results # iptables -L
>
> # EOF
>
>
> So when the hitcount gets to 4 with an incorrect password, that IP is
> dropped and my node becomes invisible. I couple that with redirecting my
> incoming port in my router. Between the two, my log is clean and clear of
> hacking attempts. If you are using a different port ON THE LOCAL MACHINE
> (not at the router) make sure you change the -dport ‘???’ entry. Doug has
> a fine HowTo on setting up iptables for Supermon. As I said, I do not
> refresh it because there is no need with a dynamic DNS at each
> router/access, provided you use the name and not an IP address. I use NoIP
> for dynamic assignments and although I have to verify once a month, it has
> never failed to update the IP within a few minutes. The NoIP system
> reminds me with an e-mail a couple of days before the confirmation is due,
> and it’s free that way.
>
> 73,
>
> Charles - NK8O
>
> > On May 17, 2018, at 7:14 AM, k6cks01 via arm-allstar <
> arm-allstar at hamvoip.org> wrote:
> >
> > That is very interesting Charles, would you be interested in sharing an
> example of your script?Rory, K5CKS
> >
> >
> > Sent via the Samsung Galaxy S®6 active, an AT&T 4G LTE smartphone
> > -------- Original message --------From: Charles Powell via arm-allstar <
> arm-allstar at hamvoip.org <mailto:arm-allstar at hamvoip.org>> Date: 5/16/18
> 9:55 PM (GMT-06:00) To: ARM Allstar <arm-allstar at hamvoip.org <mailto:
> arm-allstar at hamvoip.org>> Cc: Charles Powell <5h3dx.zinga at gmail.com
> <mailto:5h3dx.zinga at gmail.com>> Subject: Re: [arm-allstar] Firewall
> thoughts ---was:Trouble with Supermon
> > Remember it is still possible to write an IP tables rule that blocks an
> attacker after the 3rd (or whatever number you choose) attempt with an
> incorrect password It is VERY effective. A log with a brute force attack
> will have pages and pages of information from the same IP address. Between
> diversion and a good IP tables script, I see absolutely no hack attempts.
> I take that back. I had one - that was shutdown on password #4.
> >
> > 73,
> >
> > Charles - NK8O
> >
> >> On May 16, 2018, at 9:48 PM, David McGough via arm-allstar <
> arm-allstar at hamvoip.org> wrote:
> >>
> >>
> >> My opinion is that pre-shared keys for SSH are a great step in the right
> >> direction. But, leaving it on port 22 might still lead to problems.
> First,
> >> this is still a TCP port, and it can be impacted by protocol-level
> (level
> >> 3 or level 2) attacts. If nothing else, it might lead to a DoS
> condition.
> >>
> >> Second, even with pre-shared keys, the ssh daemon leaks information.
> For
> >> example, on my system with ssh passwords disabled:
> >>
> >> mcgough at david-vb:~$ telnet 192.168.232.111 222
> >> Trying 192.168.232.111...
> >> Connected to 192.168.232.111.
> >> Escape character is '^]'.
> >> SSH-2.0-OpenSSH_7.2
> >>
> >>
> >> So, with this info, I can rapidly determine that the sshd is present
> and I
> >> can determine it only seems to allow PSK authentication. So, I change
> my
> >> attack strategy!
> >>
> >>
> >> 73, David KB4FXC
> >>
> >>
> >>
> >>
> >>
> >> On Wed, 16 May 2018, "Jeff Karpinski via arm-allstar" wrote:
> >>
> >>> Really should disable password SSH logins. Limit to pre-shared keys
> and it won’t matter what bit what port you use. 22 is fine.
> >>
> >>
> >>> On May 16, 2018, at 7:18 PM, David McGough via arm-allstar <
> arm-allstar at hamvoip.org> wrote:
> >>>
> >>>
> >>> Hi Guys,
> >>>
> >>> I haven't commented much about the firewall / open ports issue, so
> >>> far...I've been really busy this week.
> >>>
> >>> Anyhow, I agree with Tony that "security by obscurity" is indeed a
> viable
> >>> strategy to reduce the number of drive-by port scans and attacks. But,
> the
> >>> ports you choose must truly be OBSCURE! For example, with a SSH server,
> >>> ports 22, 222, 2022, 2222, 4022, etc., (most everything ending in
> "22")
> >>> will get rampantly scanned!! But, put ssh on port 7589. Nada! Not a
> >>> single scan!
> >>>
> >>> There are a number of excellent tools for Linux which will help with
> >>> understanding what ports are open and the traffic on your network,
> too.
> >>> Some are: netstat, nmap and tcpdump/wireshark.
> >>>
> >>> Running a "netstat -anp" (as root) on your local Linux box show all
> the
> >>> current network bindings, including open ports, connections to ports,
> etc.
> >>>
> >>> The nmap program is a "hackers wonderland" ...nmap is a robust tool
> which
> >>> will allow you to actively probe networks looking for open ports,
> hidden
> >>> devices, etc. Just do BE AWARE that if you probe someone's network on
> the
> >>> Internet, you'll likely trip intrusion alarms!!! This type of Internet
> >>> probing is also a violation of most ISP's acceptable use policies--so
> be
> >>> careful with this tool!!!!
> >>>
> >>> tcpdump and wireshark/tshark help round out your network analysis
> toolkit!
> >>> These tools allow you to "sniff" all the traffic passing through a
> network
> >>> interface by placing the interface in promiscuous mode---meaning it
> >>> reports anything it can hear, whether destined for its IP address or
> not.
> >>> I won't get into the details about these scanners in this message or
> I'll
> >>> be writing a novel--these tools are VERY sophisticated! For example,
> you
> >>> can use them to sniff plain-text passwords or even passively monitor
> and
> >>> PLAY the actual audio traffic from Asterisk/AllStar!
> >>>
> >>>
> >>> Finally, I want to mention that firewalls are not the end-all be-all of
> >>> security and they can lull you into a FALSE sense of security! Here is
> an
> >>> example of how this is frequently true: Lets say that your system has 3
> >>> ports open: port tcp/222 (ssh), port tcp/80 (http) and port udp/4569
> >>> (IAX2). You setup a firewall and block everything, but open pinholes
> for
> >>> the 3 ports listed above. Your firewall allows everyone to connect to
> >>> these ports, no restrictions....So, what have you accomplished with
> the
> >>> firewall???? NOTHING! ....I'll end on this note as something to
> ponder.
> >>>
> >>>
> >>> 73, David KB4FXC
> >>>
> >>>
> >>>
> >>>
> >>>
> >>>
> >>> On Wed, 16 May 2018, "Tony Ross via arm-allstar" wrote:
> >>>
> >>>> While some people would criticize such alternate ports for wks
> >>> (well-known services) as "security by obscurity", it does work.
> >>>
> >>> I had a repeater owner ask for my help, as one of his irlp nodes
> seemed
> >>> to not respond to ssh client requests; he couldn't log in remotely. It
> >>> was difficult, but I eventually found a prompt. I immediately looked
> at
> >>> /var/log/* and found some very large syslog files. Looking at their
> >>> contents showed an ssh attack on port 22, so I changed the port to
> >>> something in a different range, re-started the sshd and the problem
> stopped.
> >>>
> >>> Using simple system tools such as grep, sort, awk, uniq and wc, it was
> >>> easy to find that > 3.7 million ssh attempts in 4 days from 4
> east-Asian
> >>> IP addresses had essentially crippled the system.
> >>>
> >>> It did speak well for his choice of passwords though.
> >>>
> >>> On 05/15/2018 07:19 PM, "Charles Powell via arm-allstar" wrote:
> >>>> I use a port in the 9000s because it is an unexpected service there.
> Your mileage may vary.
> >>>>
> >>>> 73,
> >>>>
> >>>> Charles - NK8O
> >>>>
> >>>>> On May 15, 2018, at 12:59 PM, Doug Crompton via arm-allstar <
> arm-allstar at hamvoip.org> wrote:
> >>>>>
> >>>>> Typically port 8080 is used but you can use high number if that does
> not
> >>>>> work. Here are three examples - 15700, 16300, 17400 but you are not
> >>>>> limited to them.
> >>>>>
> >>>>>
> >>>>> *73 Doug*
> >>>>>
> >>>>> *WA3DSP*
> >>>>>
> >>>>> *http://www.crompton.com/hamradio <http://www.crompton.com/hamradio
> >*
> >>>>>
> >>>>>
> >>>>>
> >>>
> >>> _______________________________________________
> >>>
> >>> arm-allstar mailing list
> >>> arm-allstar at hamvoip.org
> >>> http://lists.hamvoip.org/cgi-bin/mailman/listinfo/arm-allstar
> >>>
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> >>
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> >>
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> >>
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> >>
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> >>
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> >
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--
DE KA7FHA
--
Some carbon based operating systems should be left with no accessible
keyboard or mouse
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