Summary

• 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. These issues are also being referenced in the Mitre CVE as CAN-2002-1189 and CAN-2002-1190.

  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.

  This advisory is available at https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20021004-toll-fraud.

Affected Products

• This section provides details on affected products.

  Vulnerable Products

  Cisco Unity software versions 3.1.5 and lower including all 2.x versions.

  Products Confirmed Not Vulnerable

  No other Cisco products are currently known to be affected by these vulnerabilities.

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.

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 .
     

Fixed Software

• 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.

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.

URL

• https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20021004-toll-fraud

Revision History

• Revision 1.1	2002-October-05	Updated to include specific release versions and added CVE numbers
  Revision 1.0	2002-October-04	Initial Public Release

  Show Less