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, succeeded. 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.

conf=/path/to/config-file

    Use another configuration file instead of the default /etc/security/
    faillock.conf.

The options for configuring the module behavior are described in the 
faillock.conf(5) manual page. The options specified on the module command line
override the values from the configuration file.

NOTES

Configuring options on the module command line is not recommend. The /etc/
security/faillock.conf should be used instead.

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

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 specified in /
etc/security/faillock.conf or with requisite control field leaks an information
about existence or non-existence of a 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 non-existing 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 being blocked by pam_faillock.
The preauth call can be added to tell users that their logins are blocked by
the module and also to abort the authentication without even asking for
password in such case.

/etc/security/faillock.conf file example:

deny=4
unlock_time=1200
silent


/etc/pam.d/config file example:

auth     required       pam_securetty.so
auth     required       pam_env.so
auth     required       pam_nologin.so
# optionally call: auth requisite pam_faillock.so preauth
# to display the message about account being locked
auth     [success=1 default=bad] pam_unix.so
auth     [default=die]  pam_faillock.so authfail
auth     sufficient     pam_faillock.so authsucc
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 informs the authenticating user when the account is locked if
silent option is not specified in the faillock.conf.

auth     required       pam_securetty.so
auth     required       pam_env.so
auth     required       pam_nologin.so
auth     required       pam_faillock.so preauth
# optionally use requisite above if you do not want to prompt for the password
# on locked accounts
auth     sufficient     pam_unix.so
auth     [default=die]  pam_faillock.so authfail
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.

