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Private branch exchange (PBX) is an essential component that
supports the critical functions of your organization. PBXs provide a wide range of communication features that present
opportunities for unauthorized people to exploit. Failure to
protect your PBX can expose your organization to toll fraud, theft
of proprietary and confidential information, and loss of revenue.
Threats to PBXs include:
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Theft of service, such as toll fraud
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Unauthorized disclosure of critical information, such as routing
and address data
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Unauthorized data modification, such as modified billing information
or system tables to gain additional services
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Denial of service (DOS) attacks that prevent the system from performing
as intended
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Traffic analysis by an unauthorized user to observe and misuse
call information
Security measures in the PBX must prevent unauthorized
users from making fraudulent calls after they access the
system. If security restrictions are improperly implemented, incoming calls to your system can be transferred to
outgoing facilities. For example, the intruder
can configure the system to place a telephone call to a domestic
or foreign telephone number.
Topics in this section include:
Improving outbound calling security
When the outcalling feature is enabled, the system notifies subscribers
of new messages. Subscribers may want the system to call a
long-distance number or a pager number where they can receive
this notification. Consider the following options to minimize
toll fraud related to outbound calling:
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Assign the voice ports to a toll-restricted Class
of Restriction (COR) that allows calling only within a local
area.
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Add outbound calling numbers to an unrestricted calling
list for either Automatic Route Selection (ARS) or Toll Analysis.
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Do not allow callers to dial specified digits as the initial digits
of an invalid mailbox. For example, 9 is configured to request
an external line from the PBX, and the caller does not select 9. If the caller dials
the invalid mailbox 9004, the caller does not get an external line. By default,
all digits must be selected as the initial digits of an invalid
mailbox.
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Enable the Call Me Allowed field for selected subscribers only.
Set up or change a Class of Service
(COS) for the selected subscribers. Next, assign the COS to individual subscribers.
Fraudulent transfers
After users transfer to a dial tone, they can dial a trunk access
code (TAC), feature access code (FAC), or extension number. On unsecured systems, unauthorized users can make fraudulent
long-distance calls or request a company employee to transfer them
to a long-distance number.
This topic discusses the following types of transfers:
Basic Call Transfer
With Basic Call Transfer, a caller can dial any number that matches
the length of a valid extension. For example: An unauthorized caller dials
a transfer code and then the first digits of a long-distance
telephone number, such as 91809 in a 5-digit plan. The voice mail
system passes the numbers to the switch. The switch interprets
the first digit (9) as an access code and the following digits
as the prefix digit and area code. At this point, the caller enters
the remaining digits of the telephone number to complete the call.
You can restrict
call transfer to subscribers. The caller cannot make a transfer to an off-premises destination unless the digits entered
match an administered subscriber mailbox identifier, for
example, 91809.
To maintain the subscriber restriction,
do not administer mailboxes that start with the same digits as a
valid switch trunk access code. Avaya recommends that
all transfers be restricted to subscribers when Basic Call Transfer
is used.
Enhanced Call Transfer
With Enhanced Call Transfer, the voice mail system uses a digital
control link message to start the transfer. The switch verifies
that the requested destination is a valid station in the dial plan.
When a caller dials in, the system verifies that the digits entered
contain the same number of digits as administered for extension
lengths. If call transfer is restricted to subscribers, the voice
mail system also verifies that the digits entered match the extension
number of an administered subscriber.
With Enhanced Call Transfer,
the reason for a transfer is included in the control link message
that the voice mail system sends to the switch. A Call Answer call is a call that is redirected to the voice mail system
when an extension is busy or does not answer. During a Call Answer call, the voice mail system usually reports
the transfer to the switch as redirected. When a caller enters 0, zero, to Escape to Attendant, the switch uses
this reason to determine how to proceed with the call. If the reason
for the transfer is redirected, the call does not follow
the destination coverage path or the call forwarding path.
The switch does not redirect a previously redirected
call. This restriction might not be acceptable when you want the call to follow the coverage path of the transferred-to station. You can administer Enhanced Call Transfer to allow this
type of transfer.
General recommendations
Following are some general security recommendations for
PBX configuration, data, and maintenance and administration functions.
Implement the following PBX precautions to enhance the security of the entire system:
Route all calls only to their intended authorized
destinations.
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Prevent unauthorized access to, or tampering
with, existing connections or conversations.
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Prevent unauthorized disconnection of calls.
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Prevent unauthorized observation or manipulation
of the subscriber database within the PBX memory.
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Restrict the use of PBX resources and features
to authorized users and subscribers. Permit only authorized
users to modify PBX database attributes. The PBX should log
all unauthorized and authorized user attempts to do unauthorized
functions.
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Implement identification and authentication
procedures for physical access to PBX hardware and software.
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Maintain an audit trail of all security-related
incidents that occur in the switch. Protect the audit information
from unauthorized access, changes, or
destruction.
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Control privileged user access to switch functions. Give users access to only the specific functions necessary
to perform their duties.
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Define and control access to system objects,
such as software modules, routing tables, and configuration
tables.
- Ensure that the security enforcement software
is protected from external interference or tampering.
To protect the security of the PBX, perform the following activities:
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Ensure that there is a confirmation process for the authorized
disclosure or use of the PBX documents. The confirmation process
can issue and verify permits and receipts before giving access to the PBX documents.
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Ensure that the PBX is placed in a physically secure location
to ensure protection from damage and unauthorized access.
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Log all activity that starts on the PBX, and
keep a record of this log. The log can include normal daily operational routines, maintenance,
and troubleshooting procedures.
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Perform backups of the system configuration and database regularly. Store the backup files in a secure area. Permit access only to authorized personnel.
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When you plan to make changes in the PBX switch database
or operating system, review the changes. Ensure that the
changes are necessary and do not compromise controls and
integrity of the switch.
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Activate exception reports on a periodic basis. The system report identifies any deviations from the normal activity that
can indicate errors or unauthorized acts.
- Block remote maintenance access if you do not need unattended
access. Restrict dial-up access to the PBX for maintenance
and administration. Password protect the dial-up modem access.
Permit users who have access to the PBX to modify
only the data that is pertinent to their job functions.
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Provide strong physical security for the PBX software. Ensure
that PBX audit reports are shredded and destroyed properly.
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Scrutinize and validate all software upgrades. Utility upgrades
from remote contractors can give hackers unlimited access.
Emergency tasks
In an emergency such as a fire or natural disaster, complete the following tasks:
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Shut down the PBX or voice mail system immediately.
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Change all passwords.
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Report the problem immediately to your telephony company and
your equipment supplier.
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Advise all staff of the situation.
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Contact the police or authorities. Prosecutions
can deter thieves.
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Gather evidence about the emergency and its impact on your system.
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