PAM_FAILLOCK(8) Linux-PAM Manual PAM_FAILLOCK(8)
NAME
pam_faillock - Module counting authentication failures during a
specified interval
SYNOPSIS
auth ... pam_faillock.so {preauth|authfail|authsucc}
[dir=/path/to/tally-directory]
[even_deny_root] [deny=n] [fail_interval=n]
[unlock_time=n] [root_unlock_time=n]
[admin_group=name] [audit] [silent]
[no_log_info]
account ... pam_faillock.so [dir=/path/to/tally-directory]
[no_log_info]
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.
admin_group=name
If a group name is specified with this option, members of the group
will be handled by this module the same as the root account (the
options even_deny_root> and root_unlock_time will apply to them. By
default the option is not set.
MODULE TYPES PROVIDED
The auth and account module types are provided.
RETURN VALUES
PAM_AUTH_ERR
A invalid option was given, the module was not able to retrieve the
user name, no valid counter file was found, or too many failed
logins.
PAM_SUCCESS
Everything was successful.
PAM_IGNORE
User not present in passwd database.
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
FILES
/var/run/faillock/*
the files logging the authentication failures for users
SEE ALSO
faillock(8), pam.conf(5), pam.d(5), pam(8)
AUTHOR
pam_faillock was written by Tomas Mraz.
Linux-PAM Manual 04/01/2020 PAM_FAILLOCK(8)
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