[NEWS] Notify Message Spoofing Vulnerability With VoIP Phones

From: SecuriTeam (support_at_securiteam.com)
Date: 07/11/05

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Date: 11 Jul 2005 12:54:52 +0200

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      Notify Message Spoofing Vulnerability With VoIP Phones
    ------------------------------------------------------------------------

    SUMMARY

    The Session Initiation Protocol (SIP) is an application-layer control
    (signaling) protocol for creating, modifying and terminating sessions with
    one or more participants. These sessions include Internet multimedia
    conferences, Internet telephone calls, multimedia distribution and instant
    messaging. The SIP protocol is described in RFC3261 (with extensions
    contained in RFC3265).

    Due to ignoring the value of 'Call-ID' and even 'tag' and 'branch' while
    processing NOTIFY messages, VoIP-Hard-phones process are vulnerable for
    spoofing of status messages such as "Messages-Waiting".

    DETAILS

    Vulnerable Systems:
     * Cisco 7940/7960
     * Grandstream BT 100
     * Other vendors might be vulnerable as well

    According to RFC 3265, Chap 3.2 every NOTIFY has to be embedded in a
    subscription mechanism. If there isn't any knowledge of a subscription,
    the UAC has to responds with a "481 Subscription does not exist" message.

    An attacker could send "Messages-Waiting: yes" messages to all phones
    using the SIP-environment. Almost every phone processes 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 reseted Call-ID, 'branch' and
    'tag' sent by a spoofed IP-Address.

    Example:
    Attacker spoofs the SIP-Proxy's 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@10.1.1.2 SIP/2.0
      Message Header
       Via: SIP/2.0/UDP 15.1.1.12:5060;branch=000000000000000
        From: "asterisk" <sip:asterisk@10.1.1.1>;tag=000000000
         To: <sip:login@10.1.1.2>
          Contact: <sip:asterisk@10.1.1.1>
          Call-ID: 00000000000000@10.1.1.1
          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 subscription such an attack would be possible.
    Background is given by the way dialogs are described in RFC 3261 and the
    sections 5.5 and 3.2 of RFC 3265.

    ADDITIONAL INFORMATION

    The information has been provided by
    <mailto:tglemser@tele-consulting.com> Tobias Glemser .
    The original article can be found at:
    <http://pentest.tele-consulting.com/advisories/05_07_06_voip-phones.txt>
    http://pentest.tele-consulting.com/advisories/05_07_06_voip-phones.txt

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