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Limiting the Number of User Login Attempts for SSH Sessions

An administrator may login remotely to a device through SSH. Administrator credentials are stored locally on the device. If the administrator presents a valid username and password, access to the Target of Evaluation (TOE) is granted. If the credentials are invalid, the TOE allows the authentication to be retried after an interval that starts after 1 second and increases exponentially. If the number of authentication attempts exceed the configured maximum, no authentication attempts are accepted for a configured time interval. When the interval expires, authentication attempts are again accepted.

You configure the amount of time the device gets locked after failed attempts. The amount of time in minutes before the user can attempt to log in to the device after being locked out due to the number of failed login attempts specified in the tries-before-disconnect statement. When a user fails to correctly login after the number of allowed attempts specified by the tries-before-disconnect statement, the user must wait the configured amount of minutes before attempting to log in to the device again. During this lockout-period the remote session user still have access to the TOE through the console as the root user.

The lockout-period must be greater than zero. The range at which you can configure the lockout-period is one through 43,200 minutes.

You can configure the device to limit the number of attempts to enter a password while logging through SSH. Using the following command, the connection.

Here, tries-before-disconnect is the number of times a user can attempt to enter a password when logging in. The connection closes if a user fails to log in after the number specified. The range is from 2 through 10, and the default value is 3.

The local administrator access will be maintained even if the remote administration is made permanently or temporarily unavailable due to the multiple failed login attempts. The console login for local administration will be available to the users during the lockout period.

You can also configure a delay, in seconds, before a user can try to enter a password after a failed attempt.

Here, backoff-threshold is the threshold for the number of failed login attempts before the user experiences a delay in being able to enter a password again. The range is from 1 through 3, and the default value is 2 seconds.

In addition, the device can be configured to specify the threshold for the number of failed attempts before the user experiences a delay in entering the password again.

Here, backoff-factor is the length of time, in seconds, before a user can attempt to log in after a failed attempt. The delay increases by the value specified for each subsequent attempt after the threshold. The range is from 5 through 10, and the default value is 5 seconds.

You can control user access through SSH. By configuring ssh root-login deny , you can ensure the root account remains active and continues to have local administrative privileges to the TOE even if other remote users are logged off.

The SSH2 protocol provides secure terminal sessions utilizing the secure encryption. The SSH2 protocol enforces running the key-exchange phase and changing the encryption and integrity keys for the session. Key exchange is done periodically, after specified seconds or after specified bytes of data have passed over the connection. You can configure thresholds for SSH rekeying, FCS_SSHS_EXT.1.8 and FCS_SSHC_EXT.1.8. The TSF ensures that within the SSH connections the same session keys are used for a threshold of no longer than one hour, and no more than one gigabyte of the transmitted data. When either of the thresholds are reached, a rekey must be performed.

Time limit before renegotiating session keys is 1 through 1440 minutes.

Data limit before renegotiating session keys is 51200 through 4294967295 byte.


For SSH connection being unintentionally broken, we need to re-initiate the SSH connection to log in back to TOE.