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</o:shapelayout></xml><![endif]--></head><body lang=DA link="#0563C1" vlink="#954F72"><div class=WordSection1><p class=MsoNormal><span lang=EN-GB>Hi all<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-GB><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-GB>We have an Asterisk server that’s been running for a few years now without problems. We have IPTables running, as well as fail2ban and have followed all the security recommendations we have found.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-GB><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-GB>Every few weeks we get an attack that lasts about a minute or two, resulting in our AGI script being overloaded. <o:p></o:p></span></p><p class=MsoNormal><span lang=EN-GB><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-GB>What happens is that somebody seems to be trying to connect from our server – in my cdrs log I can see that they use a four digit number for source, destination and caller id, e.g.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-GB><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-GB>clid: 7321<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-GB>src: 7321<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-GB>dst: 7321<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-GB>channel: SIP/xx.xx.xx.xx-aaaaaaaa<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-GB><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-GB>xx.xx.xx.xx is our server IP. When one of our registered users makes a call the channel is SIP/yyyyyyyy-aaaaaaaa where yyyyyyyy is the SIP user ID.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-GB><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-GB>So it looks like a SIP phone trying to call itself, using our Asterisk server IP as SIP user name.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-GB><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-GB>Within a couple of minutes the attacker seems to go through some 10000 attempts, resulting in our AGI script collapsing from the load. My Asterisk full log shows something like:<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-GB><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-GB> -- Executing [7321@sip:1] Answer("SIP/xx.xx.xx.xx-b0828f20", "") in new stack<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-GB> -- Executing [7321@sip:2] AGI("SIP/ xx.xx.xx.xx -b0828f20", "agi:// xx.xx.xx.xx ") in new stack<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-GB> -- Executing [7321@sip:3] Hangup("SIP/ xx.xx.xx.xx -b6130f70", "") in new stack<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-GB> == Spawn extension (sip, 7321, 3) exited non-zero on 'SIP/ xx.xx.xx.xx -b6130f70'<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-GB> > cdr_odbc: Query Successful!<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-GB> -- AGI Script agi:// xx.xx.xx.xx completed, returning 0<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-GB><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-GB>Our AGI script refuses to call “illegal” numbers, while our Asterisk dialplan is a bit more accommodating, mostly because I have had problems figuring out the order in which to put the various rules (I might have another look at that!)<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-GB><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-GB>Does anybody know how to stop this from happening – I can’t find the attackers IP number in my logs, and these attacks happen infrequently, and are over quickly, so that I haven’t had an opportunity to run sip debug during an attack, and I don’t want to have it running all the time.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-GB><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-GB>Best regards<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-GB><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-GB>Binni<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-GB><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-GB style='mso-fareast-language:DA'>Brynjólfur Þorvarðsson<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-GB style='mso-fareast-language:DA'>IT Consultant<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-GB style='mso-fareast-language:DA'>Tlf. +45 88321688<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-GB><o:p> </o:p></span></p></div></body></html>