DISCUSSION [NIST SP 800-171 R2]

This requirement applies regardless of whether the logon occurs via a local or network connection. Due to the potential for denial of service, automatic lockouts initiated by systems are, in most cases, temporary and automatically release after a predetermined period established by the organization (i.e., a delay algorithm). If a delay algorithm is selected, organizations may employ different algorithms for different system components based on the capabilities of the respective components. Responses to unsuccessful logon attempts may be implemented at the operating system and application levels.

Further Discussion

Consecutive unsuccessful logon attempts may indicate malicious activity. Contractors can mitigate these attacks by limiting the number of unsuccessful logon attempts, typically by locking the account. A defined number of consecutive unsuccessful logon attempts is a common configuration setting. Contractors are expected to set this number at a level that fits their risk profile with the knowledge that fewer unsuccessful attempts provide higher security.

After an unsuccessful login attempt threshold is exceeded and the system locks an account, the account may either remain locked until an administrator takes action to unlock it, or it may be locked for a predefined time after which it unlocks automatically.

Example

You attempt to log on to your work computer. You mistype your password three times in a row, and an error message is generated telling you the account is locked [b]. You call your IT help desk or system administrator to request assistance. The system administrator explains that the account is locked as a result of three unsuccessful logon attempts [a]. The administrator offers to unlock the account and notes that you can wait 30 minutes for the account to unlock automatically.

Potential Considerations

Is there a defined threshold for the number of unsuccessful logon attempts for which the system takes action to prevent additional attempts [a]?

Is a mechanism for limiting the number of unsuccessful logon attempts implemented and does it use the defined threshold [b]?

Copyright

Copyright 2020, 2021 Carnegie Mellon University and The Johns Hopkins University Applied Physics Laboratory LLC.

Copyright 2021 Futures, Inc.

This material is based upon work funded and supported by the Department of Defense under Contract No. FA8702-15-D-0002 with Carnegie Mellon University for the operation of the Software Engineering Institute, a federally funded research and development center, and under Contract No. HQ0034-13-D-0003 and Contract No. N00024-13-D-6400 with the Johns Hopkins University Applied Physics Laboratory LLC, a University Affiliated Research Center.

The view, opinions, and/or findings contained in this material are those of the author(s) and should not be construed as an official Government position, policy, or decision, unless designated by other documentation.

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