13. Changing
passwords with rpasswd
The standard way to change a NIS password is to call yppasswd, on some systems this is only an alias for
passwd. This commands uses the yppasswd
protocol and needs a running rpc.yppasswdd
process on the NIS master server. The protocol has the
disadvantage, that the old password will be send in clear text over
the network. This is not so problematic, if the password change was
successfull. In this case, the old password is replaced with the
new one. But if the password change fails, an attacker can use the
clear password to login as this user. Even more worse: If the
system administrator changes the NIS password for another user, the
root password of the NIS master server is transfered in clear text
over the network. And this one will not be changed.
One solution is to not use yppasswd for changing the password.
Instead, a good alternative is the rpasswd
command from the pwdutils package.
Site Directory File Name
ftp.kernel.org /pub/linux/utils/net/NIS pwdutils-2.3.tar.gz
ftp.suse.com /pub/people/kukuk/pam/pam_pwcheck pam_pwcheck-2.2.tar.bz2
ftp.suse.com /pub/people/kukuk/pam/pam_unix2 pam_unix2-1.16.tar.bz2
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rpasswd changes passwords for user
accounts on a remote server over a secure SSL connection. A normal
user may only change the password for their own account, if the
user knows the password of the administrator account (in the moment
this is the root password on the server), he may change the
password for any account if he calls rpasswd
with the -a option.
13.1. Server
Configuration
For the server you need at first certificate, the default
filename for this is /etc/rpasswdd.pem.
The file can be created with the following command:
openssl req -new -x509 -nodes -days 730 -out /etc/rpasswdd.pem -keyout /etc/rpasswdd.pem
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A PAM configuration file for rpasswdd is
needed, too. If the NIS accounts are stored in /etc/passwd, the following is a good starting point
for a working configuration:
#%PAM-1.0
auth required pam_unix2.so
account required pam_unix2.so
password required pam_pwcheck.so
password required pam_unix2.so use_first_pass use_authtok
password required pam_make.so /var/yp
session required pam_unix2.so
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If sources for the NIS password maps are stored in another
location (for example in /etc/yp), the nisdir option of pam_unix2 can be used to find the
source files in another place:
#%PAM-1.0
auth required pam_unix2.so
account required pam_unix2.so
password required pam_pwcheck.so nisdir=/etc/yp
password required pam_unix2.so nisdir=/etc/yp use_first_pass use_authtok
password required pam_make.so /var/yp
session required pam_unix2.so
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Now start the rpasswdd daemon on the NIS
master server.
Since the password change is done with PAM modules, rpasswdd is also able to allow password changes for
NIS+, LDAP or other services supported by a PAM module.
