Tele-Consulting GmbH security | networking | training advisory 05/07/06 URL of this advisory: http://pentest.tele-consulting.com/advisories/05_07_06_voip-phones.txt Topic: Weakness in implemenation of proccessing SIP-Notify-Messages in VoIP-Phones. Summary: Due to ignoring the value of 'Call-ID' and even 'tag' and 'branch' while processing NOTIFY messages, VoIP-Hardphones process spoofed status messages like "Messages-Waiting". According to RFC 3265, Chap 3.2 every NOTIFY has to be em- bedded in a subcription mechanism. If there ain't knowledge of a subscription, the UAC has to respond with a "481 Subscription does not exist" message. All tested phones processed the "Messages-Waiting" messages without prior subscriptions anywhere. Effect: An attacker could send "Messages-Waiting: yes" messages to all phones in a SIP-environment. Almost every phone proccesses this status message and shows the user an icon or a blinking display to indicate that new messages are available on the voice box. If the attacker sends this message to many recipients in a huge environment, it would lead to server peaks as many users will call the voice box at the same time. Because there are no new voice messages as indicated by the phone the users will call the support to fix this alleged server problem. All tested phones process the message with a resetted Call-ID, 'branch' and 'tag' sent by a spoofed IP-Adress. Example: Attacker spoofs the SIP-Proxys IP, here: 10.1.1.1 Victim 10.1.1.2 UDP-Message from Attacker to Victim Session Initiation Protocol Request-Line: NOTIFY sip:login@xxxxxxxx SIP/2.0 Message Header Via: SIP/2.0/UDP 15.1.1.12:5060;branch=000000000000000 From: "asterisk" <sip:asterisk@xxxxxxxx>;tag=000000000 To: <sip:login@xxxxxxxx> Contact: <sip:asterisk@xxxxxxxx> Call-ID: 00000000000000@xxxxxxxx CSeq: 102 NOTIFY User-Agent: Asterisk PBX Event: message-summary Content-Type: application/simple-message-summary Content-Length: 37 Message body Messages-Waiting: yes\n Voicemail: 3/2\n Solution: Phones who receive a NOTIFY message to which no subscription exists, must send a "481 Subscription does not exist" response. It should be possible to use the REGISTER request as a non-SUBSCRIBE mechanism to set up a valid subscription. This would reduce the possibility of an attack in a way, that only with a sniffed and spoofed subcription such an attack would be possible. Background is given by the way dialogs are des- cribed in RFC 3261 and the sections 5.5 and 3.2 of RFC 3265. Affected products: Cisco 7940/7960 Grandstream BT 100 others will be tested in future -- Tobias Glemser TTTTTTT CCCC TT C tglemser@xxxxxxxxxxxxxxxxxxx +49 (0)7032/97580 (fon) TT C pentest.tele-consulting.com +49 (0)7032/74750 (fax) TT C TT C Tele-Consulting GmbH, Siedlerstrasse 22-24, 71126 Gaeufelden TT CCCC security | networking | training
