PAM_PWQUALITY(8) Linux-PAM Manual PAM_PWQUALITY(8)
NAME
pam_pwquality - PAM module to perform password quality checking
SYNOPSIS
pam_pwquality.so [...]
DESCRIPTION
This module can be plugged into the password stack of a given service
to provide some plug-in strength-checking for passwords. The code was
originally based on pam_cracklib module and the module is backwards
compatible with its options.
The action of this module is to prompt the user for a password and
check its strength against a system dictionary and a set of rules for
identifying poor choices.
The first action is to prompt for a single password, check its strength
and then, if it is considered strong, prompt for the password a second
time (to verify that it was typed correctly on the first occasion). All
being well, the password is passed on to subsequent modules to be
installed as the new authentication token.
The checks for strength are:
Palindrome
Is the new password a palindrome?
Case Change Only
Is the new password the the old one with only a change of case?
Similar
Is the new password too much like the old one? This is primarily
controlled by one argument, difok which is a number of character
changes (inserts, removals, or replacements) between the old and
new password that are enough to accept the new password.
Simple
Is the new password too small? This is controlled by 6 arguments
minlen, maxclassrepeat, dcredit, ucredit, lcredit, and ocredit. See
the section on the arguments for the details of how these work and
there defaults.
Rotated
Is the new password a rotated version of the old password?
Same consecutive characters
Optional check for same consecutive characters.
Too long monotonic character sequence
Optional check for too long monotonic character sequence.
Contains user name
Check whether the password contains the user's name in some form.
Dictionary check
The Cracklib routine is called to check if the password is part of
a dictionary.
These checks are configurable either by use of the module arguments or
by modifying the /etc/security/pwquality.conf configuration file. The
module arguments override the settings in the configuration file.
OPTIONS
debug
This option makes the module write information to syslog(3)
indicating the behavior of the module (this option does not write
password information to the log file).
authtok_type=XXX
The default action is for the module to use the following prompts
when requesting passwords: "New UNIX password: " and "Retype UNIX
password: ". The example word UNIX can be replaced with this
option, by default it is empty.
retry=N
Prompt user at most N times before returning with error. The
default is 1.
difok=N
This argument will change the default of 1 for the number of
changes in the new password from the old password.
The special value of 0 disables all checks of similarity of the new
password with the old password except the new password being
exactly the same as the old one.
minlen=N
The minimum acceptable size for the new password (plus one if
credits are not disabled which is the default). In addition to the
number of characters in the new password, credit (of +1 in length)
is given for each different kind of character (other, upper, lower
and digit). The default for this parameter is 8. Note that there is
a pair of length limits also in Cracklib, which is used for
dictionary checking, a "way too short" limit of 4 which is hard
coded in and a build time defined limit (6) that will be checked
without reference to minlen.
dcredit=N
(N >= 0) This is the maximum credit for having digits in the new
password. If you have less than or N digits, each digit will count
+1 towards meeting the current minlen value. The default for
dcredit is 0 which means there is no bonus for digits in password.
(N < 0) This is the minimum number of digits that must be met for a
new password.
ucredit=N
(N >= 0) This is the maximum credit for having upper case letters
in the new password. If you have less than or N upper case
letters, each upper case letter will count +1 towards meeting the
current minlen value. The default for ucredit is 0 which means
there is no bonus for upper case letters in password.
(N < 0) This is the minimum number of upper case letters that must
be met for a new password.
lcredit=N
(N >= 0) This is the maximum credit for having lower case letters
in the new password. If you have less than or N lower case
letters, each lower case letter will count +1 towards meeting the
current minlen value. The default for lcredit is 0 which means
there is no bonus for lower case letters in password.
(N < 0) This is the minimum number of lower case letters that must
be met for a new password.
ocredit=N
(N >= 0) This is the maximum credit for having other characters in
the new password. If you have less than or N other characters,
each other character will count +1 towards meeting the current
minlen value. The default for ocredit is 0 which means there is no
bonus for other characters in password.
(N < 0) This is the minimum number of other characters that must be
met for a new password.
minclass=N
The minimum number of required classes of characters for the new
password. The four classes are digits, upper and lower letters and
other characters. The difference to the credit check is that a
specific class if of characters is not required. Instead N out of
four of the classes are required. By default the check is disabled.
maxrepeat=N
Reject passwords which contain more than N same consecutive
characters. The default is 0 which means that this check is
disabled.
maxsequence=N
Reject passwords which contain monotonic character sequences longer
than N. The default is 0 which means that this check is disabled.
Examples of such sequence are '12345' or 'fedcb'. Note that most
such passwords will not pass the simplicity check unless the
sequence is only a minor part of the password.
maxclassrepeat=N
Reject passwords which contain more than N consecutive characters
of the same class. The default is 0 which means that this check is
disabled.
gecoscheck=N
If nonzero, check whether the individual words longer than 3
characters from the passwd(5) GECOS field of the user are contained
in the new password. The default is 0 which means that this check
is disabled.
dictcheck=N
If nonzero, check whether the password (with possible
modifications) matches a word in a dictionary. Currently the
dictionary check is performed using the cracklib library. The
default is 1 which means that this check is enabled.
usercheck=N
If nonzero, check whether the password (with possible
modifications) contains the user name in some form. The default is
1 which means that this check is enabled. It is not performed for
user names shorter than 3 characters.
usersubstr=N
If greater than 3 (due to the minimum length in usercheck), check
whether the password contains a substring of at least N length in
some form. The default is 0, which means this check is disabled.
enforcing=N
If nonzero, reject the password if it fails the checks, otherwise
only print the warning. The default is 1 which means that the weak
password is rejected (for non-root users).
badwords=<list of words>
The words more than 3 characters long from this space separated
list are individually searched for and forbidden in the new
password. By default the list is empty which means that this check
is disabled.
dictpath=/path/to/dict
This options allows for specification of non-default path to the
cracklib dictionaries.
enforce_for_root
The module will return error on failed check even if the user
changing the password is root. This option is off by default which
means that just the message about the failed check is printed but
root can change the password anyway. Note that root is not asked
for an old password so the checks that compare the old and new
password are not performed.
local_users_only
The module will not test the password quality for users that are
not present in the /etc/passwd file. The module still asks for the
password so the following modules in the stack can use the
use_authtok option. This option is off by default.
use_authtok
This argument is used to force the module to not prompt the user
for a new password but use the one provided by the previously
stacked password module.
MODULE TYPES PROVIDED
Only the password module type is provided.
RETURN VALUES
PAM_SUCCESS
The new password passes all checks.
PAM_AUTHTOK_ERR
No new password was entered, the username could not be determined
or the new password fails the strength checks.
PAM_AUTHTOK_RECOVERY_ERR
The old password was not supplied by a previous stacked module or
got not requested from the user. The first error can happen if
use_authtok is specified.
PAM_SERVICE_ERR
A internal error occurred.
EXAMPLES
For an example of the use of this module, we show how it may be stacked
with the password component of pam_unix(8).
#
# These lines stack two password type modules. In this example the
# user is given 3 opportunities to enter a strong password. The
# "use_authtok" argument ensures that the pam_unix module does not
# prompt for a password, but instead uses the one provided by
# pam_pwquality.
#
password required pam_pwquality.so retry=3
password required pam_unix.so use_authtok
Another example is for the case that you want to use sha256 password
encryption:
#
# These lines allow modern systems to support passwords of at least 14
# bytes with extra credit of 2 for digits and 2 for others the new
# password must have at least three bytes that are not present in the
# old password
#
password required pam_pwquality.so \
difok=3 minlen=15 dcredit=2 ocredit=2
password required pam_unix.so use_authtok nullok sha256
And here is another example in case you don't want to use credits:
#
# These lines require the user to select a password with a minimum
# length of 8 and with at least 1 digit number, 1 upper case letter,
# and 1 other character
#
password required pam_pwquality.so \
dcredit=-1 ucredit=-1 ocredit=-1 lcredit=0 minlen=8
password required pam_unix.so use_authtok nullok sha256
SEE ALSO
pwscore(1), pwquality.conf(5), pam_pwquality(8), pam.conf(5), PAM(8)
AUTHORS
Tomas Mraz <tmraz AT redhat.com>
Original author of pam_cracklib module Cristian Gafton
<gafton AT redhat.com>
Red Hat, Inc. 2020-08-03 PAM_PWQUALITY(8)
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