Nortel IP Phone Surveillance Mode

[daniel.stirnimann () csnc ch]

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# COMPASS SECURITY ADVISORY http://www.csnc.ch/
#
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# Product: IP Phone
# Vendor:  Nortel
# Subject: IP Phone Surveillance Mode
# Risk:    High
# Effect:  Currently exploitable
# Author:  Daniel Stirnimann (daniel.stirnimann (at) csnc (dot) ch)
# Date:    October, 18th 2007
#
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Introduction:
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An IP phone can be put into surveillance mode if the correct UNIStim message is sent to the IP phone. The UNIStim 
message ID must match the expected ID between the signaling server and the IP phone. The protocol uses only 16bit for 
the ID number. If a malicious user sends 65536 spoofed UNIStim message with all possible ID numbers he is able to 
successfully launch this attack.

Nortel has noted this as:
Title:  UNIStim IP Phone Remote Eavesdrop Potential Vulnerability
Number: 2007008383
http://support.nortel.com/go/main.jsp?cscat=SECUREADVISORY

Vulnerable:
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Nortel IP Phone 1140E
IP Softphone 2050
and others.

See associated products on the Nortel advisory.

Vulnerability Management:
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June 2007:    Vulnerability found
June 2007:    Nortel Security notified
October 2007: Nortel Advisory & Patches available
October 2007: Compass Security Information

Remediation:
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Follow the recommended actions for the affected systems, as identified in the Nortel Advisory.

Technical Description:
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A malicious user sends n spoofed "Open Audio Stream" messages to an IP phone which it intents to put into surveillance 
mode. If the ID of the message matches the ID number between the signaling server and the IP phone, the message is 
accepted and the audio stream is opened to the host given in the "Open Audio Stream" message.

To increase the probability of exploiting this vulnerability the number of spoofed messages need to be as close as 
possible to the maximum. The RUDP datagram uses a 32bit field for the ID number. However, the implementation of Nortel 
makes only use of 16bit. That means if we send 65536 messages with different IDs we will hit the correct ID by 100%. 
However, there is a small catch, if the number of spoofed messages is too high, the IP phone will crash and a manual 
reboot is required to bring it back online.

Reference:
http://www.csnc.ch/static/advisory/secadvisorylist.html