Securely exposing an internal server to the internet

[robheaplogin]

Hi Everyone.

I have an internal web server that I need to expose to a large range of external addresses on port 80 only, and we may or may not be able to find out all of these addresses (although we may be able to verify that these address are correct via a reverse DNS lookup), hence for all intents and purposes we will need to expose the server to the Net.

Ordinarily I would place this server in a DMZ etc, pretty straightforward, however in this instance a DMZ will be tricky.

The server is on a large server Vlan that terminates on the collapsed core, the core then routes traffic to the ASA. Now I could create a DMZ and NAT the server to the Net through the DMZ however if this server were compromised it would be able to bounce around its own Vlan (and it does need acces to other servers within its own Vlan), and possibly other Vlans within the wider network via the core.

Locking down this servers in and out traffic to the core will be tricky as constant changes will need to be made to accomodate the changing access requirements of this server.

Is there any method by which this server can be exposed to the net without leaving it  wide open, can for instance an ASA act as a reverse proxy?

[Seb Rupik]

Hi there,

Firstly do you really want to be doing external web traffic using port 80? Why not 443?

You didn't specify if it were servers or users that were connecting to your web server. If it is users, then it sounds like a good case for clientless SSL VPN :

http://www.cisco.com/c/en/us/support/docs/security/asa-5500-x-series-next-generation-firewalls/70475-webvpnasa.html

http://www.cisco.com/c/en/us/td/docs/security/asa/asa92/configuration/vpn/asa-vpn-cli/webvpn-overview.html

You may also want to put your server into a PVLAN to prevent it talking to other devices in the subnet in the event of a compromise. You could then further constrain it by using an ACL on the subnets SVI.

cheers,

Seb.

[robheaplogin]

Hi There

Unfortunately I may not have a choice over port 80 or 443, although 443 would be by far the better option.

The connection will be server to server, hence we cant use a client-side  VPN in this case.

Thanks for the PVLAN suggestion, I'll carry out some research on this..

Cheers

Rob

[Seb Rupik]

Hi Rob,

Do these remote servers come from sites you control? If so you could create IPSec tunnels between the sites.

If not, then you could try portforwarding from your ASA outside interface buit I am guessing that has already been used by something else on your network.

Which just leaves you with the option of creating a static NAT entry on your outside interface, but applying an ACL preventing access from source addresses which you have not vetted and pre-approved.

cheers,

Seb.