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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.
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