Linux pam tally2 so

Use Pam_Tally2 to Lock and Unlock SSH Failed Login Attempts

pam_tally2 module is used to lock user accounts after certain number of failed ssh login attempts made to the system. This module keeps the count of attempted accesses and too many failed attempts.

pam_tally2 module comes in two parts, one is pam_tally2.so and another is pam_tally2. It is based on PAM module and can be used to examine and manipulate the counter file. It can display user login attempts counts, set counts on individual basis, unlock all user counts.

The pam_faillock module replaces the pam_tally and pam_tally2 modules which have been deprecated in RHEL 7 and RHEL 8. It offers more flexibility and options than the two modules.

By default, pam_tally2 module is already installed on the most of the Linux distributions and it is controlled by PAM package itself. This article demonstrates on how to lock and unlock SSH accounts after reaching a certain failed number of login attempts.

How to Lock and Unlock User Accounts

Use ‘/etc/pam.d/password-auth‘ configuration file to configure login attempts accesses. Open this file and add the following AUTH configuration line to it at beginning of the ‘auth‘ section.

auth required pam_tally2.so file=/var/log/tallylog deny=3 even_deny_root unlock_time=1200

Next, add the following line to ‘account‘ section.

account required pam_tally2.so
Parameters
  1. file=/var/log/tallylog – Default log file is used to keep login counts.
  2. deny=3 – Deny access after 3 attempts and lock down user.
  3. even_deny_root – Policy is also apply to root user.
  4. unlock_time=1200 – Account will be locked till 20 Min. (remove this parameters if you want to lock down permanently till manually unlock.)

Once you’ve done with above configuration, now try to attempt 3 failed login attempts to server using any ‘username‘. After you made more than 3 attempts you will get the following message.

[[email protected] ~]# ssh [email protected] [email protected]'s password: Permission denied, please try again. [email protected]'s password: Permission denied, please try again. [email protected]'s password: Account locked due to 4 failed logins Account locked due to 5 failed logins Last login: Mon Apr 22 21:21:06 2013 from 172.16.16.52

Now, verify or check the counter that user attempts with the following command.

[[email protected] ~]# pam_tally2 --user=tecmint Login Failures Latest failure From tecmint 5 04/22/13 21:22:37 172.16.16.52

How to reset or unlock the user account to enable access again.

[[email protected] pam.d]# pam_tally2 --user=tecmint --reset Login Failures Latest failure From tecmint 5 04/22/13 17:10:42 172.16.16.52

Verify login attempt is reset or unlocked

[[email protected] pam.d]# pam_tally2 --user=tecmint Login Failures Latest failure From tecmint 0

The PAM module is part of all Linux distribution and configuration provided about should work on all Linux distribution. Do ‘man pam_tally2‘ from the command line to know more about it.

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Linux pam tally2 so

NAME

pam_tally2 - The login counter (tallying) module

SYNOPSIS

pam_tally2.so [file=/path/to/counter] [onerr=[fail|succeed]] [magic_root] [even_deny_root] [deny=n] [lock_time=n] [unlock_time=n] [root_unlock_time=n] [serialize] [audit] [silent] [no_log_info] pam_tally2 [--file /path/to/counter] [--user username] [--reset[=n]] [--quiet]

DESCRIPTION

This module maintains a count of attempted accesses, can reset count on success, can deny access if too many attempts fail. pam_tally2 comes in two parts: pam_tally2.so and pam_tally2. The former is the PAM module and the latter, a stand-alone program. pam_tally2 is an (optional) application which can be used to interrogate and manipulate the counter file. It can display users' counts, set individual counts, or clear all counts. Setting artificially high counts may be useful for blocking users without changing their passwords. For example, one might find it useful to clear all counts every midnight from a cron job. Normally, failed attempts to access 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

GLOBAL OPTIONS This can be used for auth and account module types. onerr=[fail|succeed] If something weird happens (like unable to open the file), return with PAM_SUCCESS if onerr=succeed is given, else with the corresponding PAM error code. file=/path/to/counter File where to keep counts. Default is /var/log/tallylog. audit Will log the user name into the system log if the user is not found. silent Don't print informative messages. no_log_info Don't log informative messages via syslog(3). AUTH OPTIONS Authentication phase first increments attempted login counter and checks if user should be denied access. If the user is authenticated and the login process continues on call to pam_setcred(3) it resets the attempts counter. deny=n Deny access if tally for this user exceeds n. lock_time=n Always deny for n seconds after failed attempt. unlock_time=n Allow access after n seconds after failed attempt. If this option is used the user will be locked out for the specified amount of time after he exceeded his maximum allowed attempts. Otherwise the account is locked until the lock is removed by a manual intervention of the system administrator. magic_root If the module is invoked by a user with uid=0 the counter is not incremented. The sysadmin should use this for user launched services, like su, otherwise this argument should be omitted. even_deny_root Root account can become unavailable. root_unlock_time=n This option implies even_deny_root option. Allow access after n seconds to root account after failed attempt. If this option is used the root user will be locked out for the specified amount of time after he exceeded his maximum allowed attempts. serialize Serialize access to the tally file using locks. This option might be used only for non-multithreaded services because it depends on the fcntl locking of the tally file. Also it is a good idea to use this option only in such configurations where the time between auth phase and account or setcred phase is not dependent on the authenticating client. Otherwise the authenticating client will be able to prevent simultaneous authentications by the same user by simply artificially prolonging the time the file record lock is held. ACCOUNT OPTIONS Account phase resets attempts counter if the user is not magic root. This phase can be used optionally for services which don't call pam_setcred(3) correctly or if the reset should be done regardless of the failure of the account phase of other modules. magic_root If the module is invoked by a user with uid=0 the counter is not changed. The sysadmin should use this for user launched services, like su, otherwise this argument should be omitted.

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_USER_UNKNOWN User not known.

NOTES

pam_tally2 is not compatible with the old pam_tally faillog file format. This is caused by requirement of compatibility of the tallylog file format between 32bit and 64bit architectures on multiarch systems. There is no setuid wrapper for access to the data file such as when the pam_tally2.so module is called from xscreensaver. As this would make it impossible to share PAM configuration with such services the following workaround is used: If the data file cannot be opened because of insufficient permissions (EACCES) the module returns PAM_IGNORE.

EXAMPLES

Add the following line to /etc/pam.d/login to lock the account after 4 failed logins. Root account will be locked as well. The accounts will be automatically unlocked after 20 minutes. The module does not have to be called in the account phase because the login calls pam_setcred(3) correctly. auth required pam_securetty.so auth required pam_tally2.so deny=4 even_deny_root unlock_time=1200 auth required pam_env.so auth required pam_unix.so auth required pam_nologin.so account required pam_unix.so password required pam_unix.so session required pam_limits.so session required pam_unix.so session required pam_lastlog.so nowtmp session optional pam_mail.so standard

FILES

/var/log/tallylog failure count logging file

SEE ALSO

pam.conf(5), pam.d(5), pam(8)

AUTHOR

pam_tally2 was written by Tim Baverstock and Tomas Mraz.

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