GUEST POST: More on PBX security

Those of you with an attention span will remember we talked about PBX security a little while ago and Ben and I had quite a good discussion both in the comments and on Twitter about how important it all is.

Ben blogged on it and kindly allowed me to cross-post it here. Check out more from Ben at his blog.

A couple of weeks ago Paul Brislen posted a really good post on the TUANZ blog about PABX security. It seems some criminals had used a local companies phone system to route a huge number of international calls, leaving them with a colossal ($250k!) phone bill. These attacks are increasing common, and I have heard a number of similar stories.

Phone systems increasingly rely upon IP connectivity and often interface with other business processes, putting them in the domain of IT. But even if your PABX is from 1987 (mmm beige) and hasn’t been attacked yet, doesn’t mean it won’t be.

Both Telecom NZ and TelstraClear NZ have some good advice to start with, and you might find your PABX vendor can also give expert advice. Unfortunately many PABX systems are insecure from the factory, and a number of vendors don’t do a great job with security.

In a previous role I ended up managing several PABX systems spread across multiple sites, and learnt a few lessons along the way. Here are a few tips to get you started:

Have a single point of contact for phone issues – make it easier for users to change passwords, and get questions answered.
Educate your voicemail users, and work with them to use better passwords. Avoid common sequences like 0000, 1234 etc.
Document all the things! Make sure any company policies are documented and available (think about mobile phones etc too). Putting basic manuals on your intranet can really help new users.
Even if you outsource management of the phone system, make sure someone in your organization is responsible for it. And make sure this person gets more money!
Create calling restrictions, and put appropriate limits on where each line can call. If a line is only used for calls to local, national, and Australian numbers then that is all they should be able to call (don’t forget fax/alarm lines). Whatever you do, make absolutely sure that 111 (emergency services) works from all lines.
Standardise as many things as you can. Look at setting up system-wide call bars. Blocking 0900 numbers is a good start, and if no one will ever call Nigeria, it is a good idea to bar it. Make sure these settings are part of your standard config for new/moved sites.
Work with your vendor to ensure any root/master/service/vendor passwords are complex and unique. I have seen a vendor use the same service password everywhere, until a crafty hacker cracked it and then attacked many systems. Also talk to your vendor about a maintenance contract, and ensure they will install security updates in a timely manner. Restrict any remote service access where possible.
If you use auto attendants or phone menus, make sure they are secured too. Remove any option to dial through to an extension unless you are absolutely sure it is secure.
If you have multiple sites make sure that only appropriate calls can be routed between sites. Some phone hackers have been known to abuse site-site connections to work around restrictions.
If you have lots of sites, you may not always have control over the PABX, so work with your telco and have them restrict international calls as appropriate. Put this in your contract so it happens by default when you add/move sites.
If you have a mix of PABX systems/vendors at different sites, things can get very complicated and expensive, very quickly. Work on reducing the complexity.
Practice good IT security. Most PABX’s from the last 10+ years are Windows/Linux boxes (usually unpatched..) under the hood, and can be attacked over your network too (or used to attack your internal network!).
Ensure that both billing and system logging is enabled, and monitored. Otherwise a problem won’t be spotted until the next phone bill arrives.

The most important thing to take away is an awareness of the problem. Dealing with PABX’s can be complex. Don’t be afraid to get expert help. Your telco and PABX vendor are the best places to start. If you can’t get the support you need, change to one that will. If you have any advice, please add it below.