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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.
The following products are identified as affected by this vulnerability:
* Cisco Unity software versions 3.1.5 and lower including all 2.x versions.
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. |
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Credit:
The information has been provided by Cisco Systems Product Security Incident Response Team.
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Affected Products:
The following products are affected:
* Cisco Unity software versions 3.1.5 and lower including all 2.x versions.
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
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