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AC-7: UNSUCCESSFUL LOGON ATTEMPTSL

TAILORED FOR INDUSTRIAL CONTROL SYSTEMS

  • ICS Control Baselines:
  • Low
  • Moderate
  • High

The information system:

    • a. Enforces a limit of [Assignment: organization-defined number] consecutive invalid logon attempts by a user during a [Assignment: organization-defined time period]; and
    • b. Automatically [Selection: locks the account/node for an [Assignment: organization-defined time period]; locks the account/node until released by an administrator; delays next logon prompt according to [Assignment: organization-defined delay algorithm]] when the maximum number of unsuccessful attempts is exceeded.

SUPPLEMENTAL GUIDANCE

This control 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 information systems are usually temporary and automatically release after a predetermined time period established by organizations. If a delay algorithm is selected, organizations may choose to employ different algorithms for different information system components based on the capabilities of those components. Responses to unsuccessful logon attempts may be implemented at both the operating system and the application levels.

ICS SUPPLEMENTAL GUIDANCE

Many ICS must remain continuously on and operators remain logged onto the system at all times. A “log-over” capability may be employed. Example compensating controls include logging or recording all unsuccessful login attempts and alerting ICS security personnel though alarms or other means when the number of organization-defined consecutive invalid access attempts is exceeded.

CONTROL ENHANCEMENTS

AC-7 (1) UNSUCCESSFUL LOGON ATTEMPTS | AUTOMATIC ACCOUNT LOCK

[Withdrawn: Incorporated into AC-7]. (See Above.)

AC-7 (2) UNSUCCESSFUL LOGON ATTEMPTS | PURGE/WIPE MOBILE DEVICE

NOT SELECTED FOR THE NIST ISC CONTROL SET

The information system purges/wipes information from [Assignment: organization-defined mobile devices] based on [Assignment: organization-defined purging/wiping requirements/techniques] after [Assignment: organization-defined number] consecutive, unsuccessful device logon attempts.

Supplemental Guidance:

This control enhancement applies only to mobile devices for which a logon occurs (e.g., personal digital assistants, smart phones, tablets). The logon is to the mobile device, not to any one account on the device. Therefore, successful logons to any accounts on mobile devices reset the unsuccessful logon count to zero. Organizations define information to be purged/wiped carefully in order to avoid over purging/wiping which may result in devices becoming unusable. Purging/wiping may be unnecessary if the information on the device is protected with sufficiently strong encryption mechanisms.

RELATED CONTROLS: AC-7 (2)

REFERENCES:

  • NIST Special Publication 800-82 | GUIDE TO INDUSTRIAL CONTROL SYSTEMS (ICS) SECURITY