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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:

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:

Nortel IP Phone 1140E
IP Softphone 2050
and others.

See associated products on the Nortel advisory.

Vulnerability Management:

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

Remediation:

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

Technical Description:

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