pam_pwquality - PAM module to perform password quality checking
pam_pwquality.so [
...]
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 same as 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.
- 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 the user name 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.
Only the
password module type is provided.
- 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.
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
pwscore(1),
pwquality.conf(5), ,
pam.conf(5),
PAM(8)
Tomas Mraz <
[email protected]>
Original author of
pam_cracklib module Cristian Gafton
<
[email protected]>