The following is the original english message, by firstname.lastname@example.org is the summarization of voip vulnerabilities, and we are proud to say that we have realized an attack system to validate almost all the vulnerabilities, and I think point 2 and point 3 is due to the imperfection of SIP protocol itself
1.traditional IP network is insecure,its data stream is open to the public,VoIP, which is based on IP network certainly inherits this insecurity,this situation brings lots of attacks , such as Man in middle attak,call termination, sip password violent crack ,etc.
2.SIP reuses authentication mechanism from HTTP protocol ,in fact Http authentication is totally imperfect when applied to SIP protocol,for that it is a single-direction authentication, which means that only the server authenticates the endpoints,the endpoints do not authenticate the server,this situation makes it easy to deceive endpoints because they do not authenticate any entity in the network. Pseudo call (call someone with a false user id) ,server impersontation are dangerous attacks due to this vulnerability
3. SIP communication is based on message transaction, however sip transaction mechanism is quite complicated.for example, when a stateful proxy server receives a sip request message, it firstly computes the transaction ID for this message,if the transaction ID is not existed before, this request message is regarded as a new message, the server will do a lot things for this new message: save this message, create a finite statemachine for this message, construct a provisional response message and send it back, save this response message,update the finite statemachine, decide the next hop of this request message basing on the complex routing rules,transfer the request message, create one or more client transactions for the request message …these steps surely consume lots of CPU and memory resources. as a result,the server is susceptible to DoS Attacks when a hacker continually sends large quantities of SIP request messages with different Call-ID
4.Un-encrypted media stream such as RTP data is easy to be wiretapped
5.almost all VoIP software has some code flows, in this case,even a malicious packet may bring down the server, we call this packet exception packet, in fact we have found exception packets againtst both sip servers and h.323 servers
6.voip endpoints are much more intellectualized than traditional PSTN terminals,however,when this capability is abused,a lot of malicious network attacks appear: