Broadband Advisor

7. Password management: The only identifier a VoIP consumer has is the telephone number or SIP URL and a possible password for the service. The passwords are stored in both the client and server. If passwords are storied in the server in a format that can be reversed, anyone with access to that server (or proxy or registrar) can collect the username and password pairs.

8. Permissions and privileges: Resources have to be protected both from the operating system and platform perspective and from the network perspective. VoIP services running on the platform have to consider the privileges they run with. A VoIP service does not necessarily require administrative or "root" privilege to run.

9. Crypto and randomness: In VoIP signalling, confidential data needs to be protected from eavesdropping attacks. The most common vulnerability in this category is to fail to encrypt at all, even if the encryption mechanisms are available.

10. Authentication and certificate errors: Users and devices need to be authenticated. Also, other services, such as device management, exist in VoIP devices that need user authentication. Registration hijack in SIP is a flaw in which the registrar system does not authenticate the user or device, but lets attackers spoof registration messages and reregister themselves as the valid user.

11. Error handling: One example of error handling in SIP implementations is how incorrect registration is handled. A register message with an invalid telephone number can result in a "404" error code, whereas a valid telephone number would result in a "401" error. This will let the attacker narrow down the attack to try a brute-force attack on valid accounts only, or to harvest for valid accounts for Spam over Internet Telephony (SPIT).

12. Homogeneous network: An unpredicted vulnerability in many network infrastructures is a wide dependence on a limited number of vendor brands and devices variants. If an entire network depends on one specific brand of phone, proxy or firewall, one automated attack such as a virus or worm can shut down the entire network.

13. Lacking fallback system: When the VoIP network is down, as it eventually will be, there has to be backup systems that the users can fall back to. This requires careful planning for the infrastructure.

14. Physical connection quality and packet collision: If you have packet loss in your data infrastructure, you're probably not ready for VoIP. Network latency and jitter should be minimal. All bottlenecks in the communications will immediately be revealed when VoIP is introduced, even if those weren't readily apparent with traditional data communications.

Securing VoIP Networks, is published by Addison-Wesley. Peter Thermos is CTO at Palindrome Technologies and Ari Takanen is founder and CTO at Codenomicon.