Ubuntu Manpage: pam_abl.conf - Configuration file for pam

NAME

       pam_abl.conf - Configuration file for pam_abl PAM module.

SYNOPSIS

       Configuration file for both the pam_abl(8) PAM module, and the pam_abl(1) command line
       tool.

DESCRIPTION

Rule syntax
Each rule consists of a number of space separated user clauses. A user clause specifies
the user (and service) names to match and a set of triggers. A simple example would be

*:10/1h

which means block any user () if they are responsible for ten or more failed
authentication attempts in the last hour. In place of the which matches any user a list
of usernames can be supplied like this

root|dba|admin:10/1h

which means block the users root, dba and admin if they are responsible for ten or more
failed authentication attempts in the last hour. You can also specify a service name to
match against like this

root/sshd|dba/*:3/1d

which means block the users root for service 'sshd and dba for any service if they are
responsible for three or more failed authentication attempts in the last day'. Finally you
can specify multiple triggers like this

root:10/1h,20/1d

which means 'block the user root if they are responsible for ten or more failed attempts
in the last hour or twenty or more failed attempts in the last day.

Multiple rules can be provided separated by spaces like this

*:10/1h root:5/1h,10/1d

in which case all rules that match a particular user and service will be checked. The user
or host will be blocked if any of the rule triggers matches. The sense of the user
matching can be inverted by placing a ! in front of the rule so that

!root:20/1d

is a rule which would match for all users apart from root. It is important to treat root
as a special case in the user_rule otherwise excessive attempts to authenticate as root
will result in the root account being locked out even for valid holders of root
credentials. The config file can contain any arguments that would be supplied via PAM
config. In the config file arguments are placed on separate lines. Comments may be
included after a # and line continuation is possible by placing a back slash at the end of
the line to be continued. Here is a sample /etc/security/pam_abl.conf:

# /etc/security/pam_abl.conf
debug
host_db=/var/lib/abl/hosts.db
host_purge=2d
host_rule=*:10/1h,30/1d
user_db=/var/lib/abl/users.db
user_purge=2d
user_rule=!root:10/1h,30/1d

All of the standard PAM arguments (debug, expose_account, no_warn, try_first_pass,
use_first_pass, use_mapped_pass) are accepted; with the exception of debug and no_warn
these are ignored.

The arguments that are specific to the PAM module are as follows:

db_home
Specify the directory where the Berkeley db can store it’s lock and log files. Make
sure this dir exists and is writable.

limits
It’s value should have the following syntax "<minimum>-<maximum>". If you do not block
machines that do too many attempts, the db can easily become bloated. To prevent this
we introduced this setting. As soon as there are a <maximum> number of attempts for a
user/host, the number of stored attempts for this user/host is reduced to <minimum>. A
<maximum> of 0 means no limits. Make sure that <minimum> is larger then any rule
specified. We recommend a value of "1000-1200".

host_db, user_db
Specify the name of the databases that will be used to log failed authentication
attempts. The host database is used to log the hostname responsible for a failed auth
and the user database is used to log the requested username. If host_db or user_db is
omitted the corresponding auto blacklisting will be disabled.

host_purge, user_purge
Specify the length of time for which failed attempts should be kept in the databases.
For rules to work correctly this must be at least as long as the longest period
specified in a corresponding rule. You may wish to retain information about failed
attempts for longer than this so that the pam_abl command line tool can report
information over a longer period of time. The format for this item is a number with an
optional multiplier suffix, s, m, h or d which correspond with seconds, minutes, hours
and days. To specify seven days for example one would use 7d. Note that in normal
operation pam_abl will only purge the logged data for a particular host or user if it
happens to be updating it, i.e. if that host or user makes another failed attempt. To
purge all old entries the pam_abl command line tool should be used.

host_rule, user_rule
These are the rules which determine the circumstances under which accounts are
auto-blacklisted. The host_rule is used to block access to hosts that are responsible
for excessive authentication failures and the user_rule is used to disable accounts
for which there have been excessive authentication failures. The rule syntax is
described in full below.

host_clr_cmd, host_blk_cmd, user_clr_cmd, user_blk_cmd
Deprecated for security reasons. Please use the corresponding safer option:
host_clear_cmd, host_block_cmd, user_clear_cmd, user_block_cmd

host_clear_cmd, host_block_cmd, user_clear_cmd, user_block_cmd
These specify commands that will run during a check when an item switches state since
its last check.

host_clear_cmd and user_clear_cmd will run if the host or user is currently allowed
access. host_block_cmd and user_block_cmd are run if the host or user is currently
being blocked by their respective rules.

Within the commands, you can specify substitutions with %h, %u and %s, which will be
replace with the host name, user name and service currently being checked. For
security reasons we do not run the command using the system call. We use the more
secure fork/exec solution. This means that you can’t specify input and output
redirections.

Note that this also means that no escaping is done, so if you call a shell here, you
might introduce a security problem.

The commands should follow a special syntax (you can use the command line tool with
the -d option to test the parsing of your commands) where the command and it’s
different arguments need to be enclosed in [] and all text not enclosed in [] is
simply ignored. For example: "[/usr/bin/logger] ignored [block] [user] [%u]" will run
the command "/usr/bin/logger block user <current user>". If you want to specify a [, ]
or \, you need to escape them with a \.

host_whitelist, user_whitelist
;-seperated list of hosts/users whose attempts will not be recorded. So if an attempt
is made from "10.10.10.10" for user "root" and "root" is in the whitelist, only an
attempt for his machine is recorded. If a user is whitelisted, this does not prevent
his machine from being blocked. Hosts can be specified using their IP (1.1.1.1) or
using a netmask (1.1.1.1/24)

EXAMPLE

           # /etc/security/pam_abl.conf
           debug
           host_db=/var/lib/abl/hosts.db
           host_purge=2d
           host_rule=*:10/1h,30/1d
           host_block_cmd=[/sbin/iptables] [-I] [INPUT] [-s] [%h] [-j] [DROP]
           user_db=/var/lib/abl/users.db
           user_purge=2d
           user_rule=!root:10/1h,30/1d
           user_clear_cmd=[/usr/bin/logger] [block] [user] [%u]

AUTHORS

       Lode Mertens <pam-abl@danta.be>

       Andy Armstrong <andy@hexten.net>

       Chris Tasma <pam-abl@deksai.com>

AUTHOR