[nsp] Cisco Security Advisory: Predefined Restriction Tables Allow Calls to International Operator

Fri, 4 Oct 2002 11:30:00 -0400 (EDT)

The predefined restriction tables in Cisco Unity do not block calls to the
international operator. The default configuration only blocks North American
Numbering Plan (NANP) International Direct Dial (IDD) prefixes, or those
prefixes that start with 9 011. Customers may expect that since direct dial
international calls are blocked, it is not possible for users to forward calls
to international numbers, but the loophole of the international operator is
still allowed under the predefined restriction table. This subversion can be
accomplished by anyone inside or outside of a company who is familiar with how
to configure Cisco Unity and has access to a valid system username and
password, which is further compounded by the common existence of the Example
Administrator and Example Subscriber accounts in many installations.

This vulnerability has been documented as CSCdy54570.

The following products are identified as affected by this vulnerability:

  * Cisco Unity software versions 2.x, 3.x

Unless explicitly stated otherwise, all other Cisco products are not affected.

A workaround exists for this vulnerability which is detailed in the Workarounds
section below.

This advisory is available at 
http://www.cisco.com/warp/public/707/toll-fraud-pub.shtml.

Affected Products
=================

The following products are affected:

  * Cisco Unity software versions 2.x, 3.x

Details
=======

The predefined restriction tables in Cisco Unity are for North American dial
plans and do not block calls to the international operator. The default
configuration only blocks IDD patterns that start with 9 011. This may pose a
problem because subscribers can configure call forwarding in Cisco Unity to
point to the international operator (9 00) and then place international calls.

After installing Unity, customers often ignore the Example Administrator and
Example Subscriber accounts. These can be exploited by dialing into Cisco
Unity, logging into the accounts with the default extension and password, and
configuring it to call forward to the international operator or other toll
number.

Two other scenarios in which this could happen are:

 1. Internal users can set their own Cisco Unity mailboxes to forward to
    international numbers or toll numbers.
 2. External callers could log into a poorly password protected mailbox (for
    example: password=1234), and forward to international numbers or toll
    numbers.

This vulnerability has been documented as CSCdy54570.

Impact
======

The predefined restriction tables within the Cisco Unity configuration allows
direct dialing of the international operator or other toll calls which may not
be desired. Due to the existence of well known default user accounts,
successful exploitation of those default accounts or policies allowing weak
passwords on accounts can result in toll fraud which may go unnoticed until the
end of a billing cycle.

Software Versions and Fixes
===========================

The default configuration of Cisco Unity will be modified to disallow
forwarding to the international operator in future versions, however a software
upgrade is not necessary in order to mitigate the vulnerability.

Obtaining Fixed Software
========================

As the fix for this vulnerability is a default configuration change, and a
workaround is available, a software upgrade is not required to address this
vulnerability. However, if you have a service contract, and wish to upgrade to
unaffected code, you may obtain upgraded software through your regular update
channels once that software is available. For most customers, this means that
upgrades should be obtained through the Software Center on Cisco's Worldwide
Web site at http://www.cisco.com/.

If you need assistance with the implementation of the workarounds, or have
questions on the workarounds, please contact the Cisco Technical Assistance
Center (TAC).

Cisco TAC contacts are as follows:

  * +1 800 553 2447 (toll free from within North America)
  * +1 408 526 7209 (toll call from anywhere in the world)
  * e-mail: tac@cisco.com

See http://www.cisco.com/warp/public/687/Directory/DirTAC.shtml for additional
TAC contact information, including special localized telephone numbers and
instructions and e-mail addresses for use in various languages.

Please do not contact either "psirt@cisco.com" or "security-alert@cisco.com"
for software upgrades.

Workarounds
===========

Adding additional dial strings to the restriction tables will prevent Unity
from trying to place a toll call. For example, to block all international calls
as well as toll calls while still retaining the ability to dial locally, the
following restriction table entries might be useful for installations in North
America:

91???????*     No 
90*            No 
9??????????    Yes
9???????       Yes

In the example above, the first line will match and block all domestic (US)
toll calls. The second line will match and block all international calls
including the international operator. The third line matches and allows local
calls. This line is not necessary if your area does not use local area codes.
The fourth line matches and allows local calls. This or other locally
applicable lines should be applied to all restriction tables. Note that some
locations use 10 digit dialing for non-toll calls. In those locations the
restrictions should allow specific non-toll prefixes while blocking all other
toll prefixes.

For installations outside of North America where the dial plans vary from the
above example, the restriction table entries will be different. Information to
assist in creating restriction tables can be found in the section entitled
"Restriction Tables" in the Cisco Unity System Administration Guide.

In addition, Cisco recommends the protection of the Example Administrator and
the Example Subscriber accounts. These accounts at a minimum should have their
default extension and default password changed. This should be done as part of
tightening the security on your Cisco Unity system. For more details refer to: 
White Paper: Best Practices for Cisco Unity 3.0

It is also possible to remove the Example Administrator and the Example
Subscriber accounts. Care must be taken in removing the Example Administrator
account, as removing it improperly could result in the Cisco Unity server no
longer functioning properly. The process to remove those accounts has been
documented at 
http://www.cisco.com/warp/public/788/AVVID/remove_example_admin.html

Other methods of mitigating the risk are:

 1. If Unity is integrated with a Call Manager, adding a route filter to the
    route pattern Unity uses to dial to the Public Switched Telephone Network
    (PSTN) will prevent calls to the international operator.
 2. Restricting Unity from placing calls to the PSTN if that capability is not
    needed.
 3. Apply a good password policy. Refer to the white paper on Best Practices
    for Cisco Unity 3.0

Exploitation and Public Announcements
=====================================

The Cisco PSIRT has been made aware of malicious use of the vulnerability
described in this advisory. Customers are advised to perform the steps as
described in the Workarounds section in order to prevent misuse of their Cisco
Unity servers.

Status of This Notice: FINAL
============================

This is a final notice. Although Cisco cannot guarantee the accuracy of all
statements in this notice, all of the facts have been checked to the best of
our ability. Cisco does not anticipate issuing updated versions of this notice
unless there is some material change in the facts. Should there be a
significant change in the facts, Cisco may update this notice.

Distribution
============

This notice will be posted on Cisco's Worldwide Web site at 
http://www.cisco.com/warp/public/707/toll-fraud-pub.shtml. 
In addition to Worldwide Web posting, a text version of this notice is 
clear-signed with the Cisco PSIRT PGP key and is posted to the following 
e-mail and Usenet news recipients:

  * cust-security-announce@cisco.com
  * bugtraq@securityfocus.com
  * full-disclosure@lists.netsys.com
  * first-teams@first.org (includes CERT/CC)
  * cisco@spot.colorado.edu
  * cisco-nsp@puck.nether.net
  * comp.dcom.sys.cisco
  * firewalls@lists.gnac.com
  * Various internal Cisco mailing lists

Future updates of this notice, if any, will be placed on Cisco's Worldwide Web
server, but may or may not be actively announced on mailing lists or
newsgroups.

Users concerned about this problem are encouraged to check the URL given above
for any updates.

Revision History
================

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Cisco Security Procedures
=========================

Complete information on reporting security vulnerabilities in Cisco products,
obtaining assistance with security incidents, and registering to receive
security information from Cisco, is available on Cisco's Worldwide Web site at 
http://www.cisco.com/warp/public/707/sec_incident_response.shtml. This includes
instructions for press inquiries regarding Cisco security notices. All Cisco
Security Advisories are available at http://www.cisco.com/go/psirt/.

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This notice is Copyright 2002 by Cisco Systems, Inc. This notice may be
redistributed freely after the release date given at the top of the text,
provided that redistributed copies are complete and unmodified, and include all
date and version information.

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