I run my own sip server (asterisk). Apparently my sip server allows to perform an INVITE without doing any REGISTER first. This leads to lots of unsuccessful attacks on my server. IS there any way to allow INVITE requests only from a successfully REGISTERed clients? Through asterisk or iptables?
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My study so far tells me that REGISTER is only for asterisk to reach or forward the INVITES but not to authenticate an INVITE request. When an INVITE comes, asterisk tries to check the given user name and if its a valid one, it sends a 407 (Authentication required) back to the client. Then client inserts the password (encrypted) in the response and sends INVITE2 to server. Now server authenticates the user and when credentials match, proceeds with establishing the call.
Conclusion: An INVITE has no relation with REGISTER and so my idea of restricting only REGISTERED clients to send an INVITE is not possible.
As a workaround, I have written my own script. Source is at https://github.com/naidu/JailMe