Thursday, 14 May 2009

Log Attack Attempts

While I was answering emails and writing another blog post, I was reminded that lots of people ask me about the seriousness of the threat of attack as they are sceptical. So, I decided to turn on additional logging on my router to view all incoming traffic to see what it is blocking silently. I can tell you that in 2 hours on my home connection here I have had 22 different IP addresses making 47 different attempts to connect to me. One tried to launch a Denial-of-Service (DoS) attack on my web server three times (unsuccessfully), and another attached to my web server to view the options available and didn't bother retrieving any pages - this is a classic sign of footprinting before an attack. The first was host and the second was

What were the other 20 connection attempts? Well I don't actually have anything else open on my network, but by logging all connection attempts I can view what people are trying. One tried to connect to port 3389 (Microsoft's RDP port) and then 3306 (mySQL), which is maybe a slightly strange combination - Microsoft's Terminal Services machine running open source mySQL? There were 4 attempts to connect to port 135 (Microsoft's DCOM Service Control Manager), 3 attempts to connect to port 445 (Microsoft's Directory Services), 4 attempts to connect to port 3128 (Active API Server), 2 attempts at port 2967 (SSC-Agent), 3 attempts at port 8000 (iRDMI, but sometimes used as secondary web port), and so on.

There are well-known attacks for these ports that are supported under tools such as the Metasploit Framework. So, this is an unlisted private broadband connection that had 22 attack attempts in 2 hours. What people have to realise is that computers are very good at doing repetitive, mind numbing tasks. You can scan a range of IP addresses very easily from tools that you can download for free. If they get a reply to these sweeps then they can investigate. If your firewall isn't blocking all these ports then you will get attacks. That's not the end of the story though. If your firewall responds to these connection attempts then you are telling the attacker that there is a machine there to be attacked. How do you stop this?

When one machine tries to connect to another over the network several things can happen, but the two main ones are: the port is open and a service is running on it accepting connections, in which case the connection will be successful; secondly, the port is not open and the service that would use that port isn't running, in which case your machine will respond telling the originating host that it isn't listening on that port. Now it is worth running a full port scan to find out what it is listening to (and yes, before you ask, you can defeat the port scanning alerts on firewalls fairly easily in most cases). This is what you must stop by stealthing unused ports, i.e. if a connection attempt comes in on a port you aren't using, discard the packet and do not reply. Most firewalls will do this for you if you configure it, but make sure that it is set up correctly.

One final note, always log attack attempts and never set your firewall to reply to pings on the WAN port!

P.S. I've had 7 more since starting to write this post.


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