Network WLAN Bridge Management Security Technical Implementation Guide

Password complexity, or strength, is a measure of the effectiveness of a password in resisting attempts at guessing and brute-force attacks. Password length is one factor of several that helps to determine strength and how long it takes to crack a password. The shorter the password, the lower the number of possible combinations that need to be tested before the password is compromised. Use of more characters in a password helps to exponentially increase the time and/or resources required to compromise the password.

Network devices not protected with strong password schemes provide the opportunity for anyone to crack the password and gain access to the device, which can result in loss of availability, confidentiality, or integrity of network traffic. Many default vendor passwords are well known or easily guessed; therefore, not removing them prior to deploying the network device into production provides an opportunity for a malicious user to gain unauthorized access to the device.

All network devices must present a DoD-approved warning banner prior to a system administrator logging on. The banner should warn any unauthorized user not to proceed. It also should provide clear and unequivocal notice to both authorized and unauthorized personnel that access to the device is subject to monitoring to detect unauthorized usage. Failure to display the required logon warning banner prior to logon attempts limits DoD's ability to prosecute unauthorized access and also presents the potential for criminal and civil liability for systems administrators and information systems managers. In addition, DISA's ability to monitor the device's usage is limited unless a proper warning banner is displayed. DoD CIO has issued new, mandatory policy standardizing the wording of "notice and consent" banners and matching user agreements for all Secret and below DoD information systems, including stand-alone systems by releasing DoD CIO Memo, "Policy on Use of Department of Defense (DoD) Information Systems Standard Consent Banner and User Agreement", dated 9 May 2008. The banner is mandatory and deviations are not permitted except as authorized in writing by the Deputy Assistant Secretary of Defense for Information and Identity Assurance. Implementation of this banner verbiage is further directed to all DoD components for all DoD assets via USCYBERCOM CTO 08-008A.

To ensure individual accountability and prevent unauthorized access, administrators must be individually identified and authenticated. Individual accountability mandates that each administrator is uniquely identified. A group authenticator is a shared account or some other form of authentication that allows multiple unique individuals to access the network device using a single account. If a device allows or provides for group authenticators, it must individually authenticate administrators prior to implementing group authenticator functionality. Some devices may not have the need to provide a group authenticator; this is considered a matter of device design. Where the device design includes the use of a group authenticator, this requirement will apply. This requirement applies to accounts created and managed on or by the network device.

Without generating audit records that are specific to the security and mission needs of the organization, it would be difficult to establish, correlate, and investigate the events relating to an incident or identify those responsible for one. Audit records can be generated from various components within the network device (e.g., module or policy filter).

Without authenticating devices, unidentified or unknown devices may be introduced, thereby facilitating malicious activity. Bidirectional authentication provides stronger safeguards to validate the identity of other devices for connections that are of greater risk. A local connection is any connection with a device communicating without the use of a network. A network connection is any connection with a device that communicates through a network (e.g., local area or wide area network, internet). A remote connection is any connection with a device communicating through an external network (e.g., the internet). Because of the challenges of applying this requirement on a large scale, organizations are encouraged to only apply the requirement to those limited number (and types) of devices that truly need to support this capability.

Authentication for administrative (privileged level) access to the device is required at all times. An account can be created on the device's local database for use when the authentication server is down or connectivity between the device and the authentication server is not operable. This account is referred to as the account of last resort since it is intended to be used as a last resort and when immediate administrative access is absolutely necessary. The account of last resort logon credentials must be stored in a sealed envelope and kept in a safe. The safe must be periodically audited to verify the envelope remains sealed. The signature of the auditor and the date of the audit should be added to the envelope as a record. Administrators should secure the credentials and disable the root account (if possible) when not needed for system administration functions.

By limiting the number of failed login attempts, the risk of unauthorized system access via user password guessing, otherwise known as brute forcing, is reduced.

If Network Time Protocol is not authenticated, an attacker can introduce a rogue NTP server. This rogue server can then be used to send incorrect time information to network devices, which will make log timestamps inaccurate and affect scheduled actions. NTP authentication is used to prevent this tampering by authenticating the time source.

A replay attack may enable an unauthorized user to gain access to the application. Authentication sessions between the authenticator and the application validating the user credentials must not be vulnerable to a replay attack. An authentication process resists replay attacks if it is impractical to achieve a successful authentication by recording and replaying a previous authentication message. Techniques used to address this include protocols using nonces (e.g., numbers generated for a specific one-time use) or challenges (e.g., TLS, WS_Security). Additional techniques include time-synchronous or challenge-response one-time authenticators.

Changes to the hardware or software components of the network device can have significant effects on the overall security of the network. Therefore, only qualified and authorized individuals should be allowed administrative access to the network device for implementing any changes or upgrades. This requirement applies to updates of the application files, configuration, ACLs, and policy filters.

The loss of connectivity to a particular authoritative time source will result in the loss of time synchronization (free-run mode) and increasingly inaccurate time stamps on audit events and other functions. Multiple time sources provide redundancy by including a secondary source. Time synchronization is usually a hierarchy; clients synchronize time to a local source while that source synchronizes its time to a more accurate source. The network device must use an authoritative time server and/or be configured to use redundant authoritative time sources. This requirement is related to the comparison done in CCI-001891. DoD-approved solutions consist of a combination of a primary and secondary time source using a combination or multiple instances of the following: a time server designated for the appropriate DoD network (NIPRNet/SIPRNet); United States Naval Observatory (USNO) time servers; and/or the Global Positioning System (GPS). The secondary time source must be located in a different geographic region than the primary time source.