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Limiting the Number of User Login Attempts for SSH Sessions

 

A remote administrator may login to a device through SSH. Administrator credentials are stored locally on the device. If the remote administrator presents a valid username and password, access to the 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 can configure the device to limit the number of attempts to enter a password while logging through SSH. Using the following command, the connection can be terminated if a user fails to login after a specified number of attempts:

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 1 through 10, and the default value is 10.

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. Use the backoff-factor option to specify the length of the delay in seconds. 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.

The SSHv2 protocol provides secure terminal sessions utilizing the secure encryption. The SSHv2 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.