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Re: A Vonage VOIP 3-way call CID Spoofing Vulnerability
From: Lucky 225 <Lucky225 () 2600 COM>
Date: 21 Aug 2003 06:32:25 -0000

In-Reply-To: <20030814000221.10408.qmail () www securityfocus com>

Sorry but simply calling a phone number and then 3-waying another number 
does not spoof caller id as the first number you called, at least not in 
my experience, I do know however that if you call one phone number, flash 
over and hit #90+1+npa+number# it will send that person off to the number 
you dialed(known as a call transfer) and the first number will show up as 
caller ID to the person you transfered them to, but since they are 
essentially the people calling the person you call transfered them too 
what's the difference? my only bitch about that would be privacy concerns 
like if you called someone w/ complete blocking on their line and then 
courtesy call transfered them to another # and now that other # has their 
phone number, it also gets annoying when miliwatt test numbers start 
calling your house at odd hours of the night.  Another thing odd about 
vonage is they only send your vonage number as caller ID and flex ANI, the 
real time ANI seems to be a new york phone number in the 646 areacode, try 
calling 800-444-4444 from a vonage fone to see this.

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From: Nathan Wosnack <nathan () hypervivid com>
To: bugtraq () securityfocus com
Subject: A Vonage VOIP 3-way call CID Spoofing Vulnerability

Original Advisory: Wednesday, August 13, 2003

Severity: Medium - High

Description: An attacker using the VOIP (Voice Over IP) carrier Vonage, 
has the ability to spoof the caller ID of a called party through the 
way calling feature. This trick essentially acts similar to a POTS-based 
diverter, as it allows the attacker to carry out illicit telephone 
activities while hiding his or her phone number.

Version: This was tested using Cisco Systems' ATA 186 VOIP hardware on 
Vonage carrier.

Author:  Nathan Wosnack 

Vonage Background:

"Using an existing high-speed Internet connection, Vonage technology 
enables anyone to make and receive phone calls - worldwide - with a touch-
tone telephone. Offering quality phone service bundled with enhanced IP 
communications services, our interactive communications portal is a 
gateway to advanced features only available through digital telephone 
service. Utilizing our global network and advanced routing technologies, 
Vonage offers an innovative, feature-rich and cost effective alternative 
to traditional telephony services." 

Description of the problem:

By using SIP-enabled voice over IP (VOIP) hardware such as the Cisco ATA 
186 Analog Telephone Adaptor, it's possible to spoof the caller 
identification that shows up on a call. The attacker only needs to call 
a regular phone line (POTS - plain old telephone service), place the 
caller on hold, flash over to a dial tone using the threeway call 
and then call a second party for this to work. The caller ID information 
that tends to show up is the first called party's telephone number with 
either their name listed or "unknown name" showing on a conventional 
caller-id enabled telephone. The opportunity for abuse is high and could 
allow the determined attacker to social engineer your telephone, cable, 
utility company into modifying your services. Since many companies only 
require the person's name, address, and caller id for account 
authentication, this vulnerability helps the attacker. The other 
opportunities this vulnerability gives the attacker is the ability to 
spoof anyone's caller id information for phone hacking (often 
called "phreaking"); such as breaking into voice mail accounts and PBX 
exploitation for the purpose of proprietary information gathering and 
telephone fraud. 

Solutions to the problem:

This issue is something that Vonage will need to investigate on their 
The proper routing of caller id information after a third-party call is 
initiated is the problem, and needs to be resolved by the Vonage IT staff 
figuring out why their VOIP switching equipment doesn't pass this data 
properly. The Hypervivid Solutions staff has contacted Vonage directly 
about this issue, so it can hopefully be resolved shortly. 

For everyone else, your best defense is to be aware of who is calling 
If you happen to receive a phone call from an unknown party who wants to 
place you on hold, hang up immediately and then call them back.
If you hear a recording telling you the number is not in service, then 
you've likely reached a Vonage gateway number, which mean you were likely 
called by someone attempting to exploit this Vonage VOIP vulnerability.


In the past year, Voice over IP telephony has seen many security issues. 
The voip issues range from vendor implementations of the Session 
Initiation Protocol (SIP), problems with remote-accessible code which can 
be exploited to cause a denial of service, voip phones that are weak in 
ways that facilitate man-in-the-middle attacks directed at intercepting 
telephone traffic, and most recently 3-way caller ID spoofing on Vonage.

When the information security community works closely with vendors and 
carriers, these problems can be resolved quickly and efficiently enough 
limit or even eliminate any abuse by phone phreaks and criminals.

Related Links:

http://www.hypervivid.com/ - Information, Telecom and Wireless Security 
Consulting Firm.

Vendor Contact:

http://www.cisco.com/ - Cisco Systems, Inc. Manufacturer.
http://www.vonage.com/ - American Voip telecom carrier.

Have any questions or comments?
e-mail: advisories () hypervivid com 

Copyright © 2003, Hypervivid Solutions Incorporated. All Rights Reserved.

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