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.
[edit system login] security-administrator@host:fips# set retry-options lockout-period number
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.
[edit system login] security-administrator@host:fips# set retry-options tries-before-disconnect number
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.
[edit system login] security-administrator@host:fips# set retry-options backoff-threshold number
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.
[edit system login] security-administrator@host:fips# set retry-options backoff-factor number
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.
[edit system] security-administrator@host:fips# set services ssh root-login deny
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.
[edit system] security-administrator@host:fips# set services ssh rekey time-limit number
Time limit before renegotiating session keys is 1 through 1440 minutes.
[edit system] security-administrator@host:fips# set services ssh rekey data-limit number
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.