pam_faillock ? Module counting authentication failures during a specified
interval

-------------------------------------------------------------------------------

DESCRIPTION

This module maintains a list of failed authentication attempts per user during
a specified interval and locks the account in case there were more than deny
consecutive failed authentications.

Normally, failed attempts to authenticate root will not cause the root account
to become blocked, to prevent denial-of-service: if your users aren't given
shell accounts and root may only login via su or at the machine console (not
telnet/rsh, etc), this is safe.

OPTIONS

{preauth|authfail|authsucc}

    This argument must be set accordingly to the position of this module
    instance in the PAM stack.

    The preauth argument must be used when the module is called before the
    modules which ask for the user credentials such as the password. The module
    just examines whether the user should be blocked from accessing the service
    in case there were anomalous number of failed consecutive authentication
    attempts recently. This call is optional if authsucc is used.

    The authfail argument must be used when the module is called after the
    modules which determine the authentication outcome, failed. Unless the user
    is already blocked due to previous authentication failures, the module will
    record the failure into the appropriate user tally file.

    The authsucc argument must be used when the module is called after the
    modules which determine the authentication outcome, succeded. Unless the
    user is already blocked due to previous authentication failures, the module
    will then clear the record of the failures in the respective user tally
    file. Otherwise it will return authentication error. If this call is not
    done, the pam_faillock will not distinguish between consecutive and
    non-consecutive failed authentication attempts. The preauth call must be
    used in such case. Due to complications in the way the PAM stack can be
    configured it is also possible to call pam_faillock as an account module.
    In such configuration the module must be also called in the preauth stage.

dir=/path/to/tally-directory

    The directory where the user files with the failure records are kept. The
    default is /var/run/faillock.

audit

    Will log the user name into the system log if the user is not found.

silent

    Don't print informative messages. This option is implicite in the authfail
    and authsucc functions.

no_log_info

    Don't log informative messages via syslog(3).

deny=n

    Deny access if the number of consecutive authentication failures for this
    user during the recent interval exceeds n. The default is 3.

fail_interval=n

    The length of the interval during which the consecutive authentication
    failures must happen for the user account lock out is n seconds. The
    default is 900 (15 minutes).

unlock_time=n

    The access will be reenabled after n seconds after the lock out. The
    default is 600 (10 minutes).

    If the n is set to never or 0 the access will not be reenabled at all until
    administrator explicitly reenables it with the faillock command. Note
    though that the default directory that pam_faillock uses is usually cleared
    on system boot so the access will be also reenabled after system reboot. If
    that is undesirable a different tally directory must be set with the dir
    option.

    Also note that it is usually undesirable to permanently lock out the users
    as they can become easily a target of denial of service attack unless the
    usernames are random and kept secret to potential attackers.

even_deny_root

    Root account can become locked as well as regular accounts.

root_unlock_time=n

    This option implies even_deny_root option. Allow access after n seconds to
    root account after the account is locked. In case the option is not
    specified the value is the same as of the unlock_time option.

NOTES

pam_faillock setup in the PAM stack is different from the pam_tally2 module
setup.

The individual files with the failure records are created as owned by the user.
This allows pam_faillock.so module to work correctly when it is called from a
screensaver.

Note that using the module in preauth without the silent option or with
requisite control field leaks an information about existence or non-existence
of an user account in the system because the failures are not recorded for the
unknown users. The message about the user account being locked is never
displayed for nonexisting user accounts allowing the adversary to infer that a
particular account is not existing on a system.

EXAMPLES

Here are two possible configuration examples for /etc/pam.d/login. They make
pam_faillock to lock the account after 4 consecutive failed logins during the
default interval of 15 minutes. Root account will be locked as well. The
accounts will be automatically unlocked after 20 minutes.

In the first example the module is called only in the auth phase and the module
does not print any information about the account blocking by pam_faillock. The
preauth call can be added to tell the user that his login is blocked by the
module and also to abort the authentication without even asking for password in
such case.

auth     required       pam_securetty.so
auth     required       pam_env.so
auth     required       pam_nologin.so
# optionally call: auth requisite pam_faillock.so preauth deny=4 even_deny_root unlock_time=1200
# to display the message about account being locked
auth     [success=1 default=bad] pam_unix.so
auth     [default=die]  pam_faillock.so authfail deny=4 even_deny_root unlock_time=1200
auth     sufficient     pam_faillock.so authsucc deny=4 even_deny_root unlock_time=1200
auth     required       pam_deny.so
account  required       pam_unix.so
password required       pam_unix.so shadow
session  required       pam_selinux.so close
session  required       pam_loginuid.so
session  required       pam_unix.so
session  required       pam_selinux.so open


In the second example the module is called both in the auth and account phases
and the module gives the authenticating user message when the account is locked

auth     required       pam_securetty.so
auth     required       pam_env.so
auth     required       pam_nologin.so
auth     required       pam_faillock.so preauth silent deny=4 even_deny_root unlock_time=1200
# optionally use requisite above if you do not want to prompt for the password
# on locked accounts, possibly with removing the silent option as well
auth     sufficient     pam_unix.so
auth     [default=die]  pam_faillock.so authfail deny=4 even_deny_root unlock_time=1200
auth     required       pam_deny.so
account  required       pam_faillock.so
# if you drop the above call to pam_faillock.so the lock will be done also
# on non-consecutive authentication failures
account  required       pam_unix.so
password required       pam_unix.so shadow
session  required       pam_selinux.so close
session  required       pam_loginuid.so
session  required       pam_unix.so
session  required       pam_selinux.so open


AUTHOR

pam_faillock was written by Tomas Mraz.

