[Oisf-users] Suricata Stopping Sophos Web GUI on TCP Port 4444

Wed Mar 14 06:07:01 UTC 2018

It is a Ubuntu linux appliance running Suricata.  I set the MTU 1400 from the MTU 1500 it was set at and I kinds of bad things started happening like losing connections.

Leonard

 From:   Chris Boley <ilgtech75 at gmail.com> 
 To:   Leonard Jacobs <ljacobs at netsecuris.com> 
 Cc:   Open Information Security Foundation <oisf-users at lists.openinfosecfoundation.org> 
 Sent:   3/13/2018 8:59 PM 
 Subject:   Re: [Oisf-users] Suricata Stopping Sophos Web GUI on TCP Port 4444 

Ok, thanks Leonard, just to rule it out, from whatever node you’re sourcing the traffic from; I’d have a look at setting that MTU per my suggestion. If it’s a windows box, there’s a netsh command to set mtu on an interface temporarily. If you still have the same issues you can rule out it being a simple networking related problem induced via af-packet copying the tunnel through Suri and more something else. It’s a quick 2 mins check and is at least one data point to rule out.

Best,
CB

On Tue, Mar 13, 2018 at 9:45 PM Leonard Jacobs <ljacobs at netsecuris.com> wrote:

af-packet in copy mode.  Inline IPS.  Not using IPtables.  I don't like that mode of IPS

Leonard

 From:   Chris Boley <ilgtech75 at gmail.com> 
 To:   <ljacobs at netsecuris.com> 
 Cc:   Open Information Security Foundation <oisf-users at lists.openinfosecfoundation.org> 
 Sent:   3/13/2018 8:31 PM 
 Subject:   Re: [Oisf-users] Suricata Stopping Sophos Web GUI on TCP Port 4444 

leonard, Suricata is running as an in-line bridge or zero-copy style install?

Pure speculation here:
 I’m suspecting that it’s causing packet fragmentation due to tcp-mss growing during ssl sessions within/over the vpn tunnel. I’m not sure how Suricata is causing that, but as a test you might try manually adjusting your mtu on your client interface to something like:

sudo ip link set dev eth0 mtu 1400
sudo iptables -A OUTPUT -p tcp --tcp-flags SYN,RST SYN -o eth0 -j TCPMSS --clamp-mss-to-pmtu 

That should let you squeeze the SSL session through the tunnel.

If not, I'm out of ideas.  :)
Good luck,
CB

On Tue, Mar 13, 2018 at 9:14 PM Leonard Jacobs <ljacobs at netsecuris.com> wrote:

Why would Suricata be stopping communications to Sophos Web GUI on TCP Port 4444 through an IPSec VPN Tunnel?

The weird thing about this is packet captures on both sides of tunnel from the firewalls don't show the traffic being blocked or dropped.  I disconnect the wan connection from Suricata appliance and connect directly to the firewall and everything works.  Suricata running on the outside of the firewall.

In suricata.yaml, I put this HTTP_PORTS: "[80,443,4444]" and it still does not work.  Does the problem have something to do with how Suricata interacts with the IPSec tunnel?  But this does not make any sense because the tunnel comes up and I can even Putty into the firewall command line console and ping the firewall through the tunnel.  For some reason, Suricata does not like ports 4444 and 443 to the private ip address of the firewall through the tunnel.

Thanks.

Leonard

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