SIP-based systems, including SIP proxies, SIP phones, and media gateways, are very vulnerable to various types of signaling manipulation attacks. This is especially true of systems using UDP, which are easy to trick into accepting spoofed packets. The registration process, even when it uses authentication, can be attacked , resulting in lost or otherwise manipulated calls.
Other types of attacks, such as tearing down active calls or rebooting SIP phones, are also easy to perform.
Because it can occur in virtually any VoIP deployment, RTP manipulation is an extremely serious type of attack. Very little RTP is encrypted, so if an attacker has access to the portion of the network carrying RTP, she can easily manipulate it by adding noise, words, or other background noise.