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

Chris Boley ilgtech75 at gmail.com
Wed Mar 14 01:31:08 UTC 2018

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

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

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

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

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

> 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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