Weak password encryption used when changing NIS user password

This document (7023131) is provided subject to the disclaimer at the end of this document.

Environment

SUSE Linux Enterprise Server 15
SUSE Linux Enterprise Server 12

SUSE Linux Enterprise Server 11

Situation

The system administrator of a SLES 12 / SLES 15 system has set pam to use sha512 encryption with the following command:

pam-config -a --unix --unix-sha512

Which successfully resulted in changes to the /etc/pam.d/common-* files, including this line from common-password:

password     required     pam_unix.so   use_authtok debug sha512 nis try_first_pass

For the most part, this has taken effect. However, when NIS users change their password with the passwd command, the new password hash gets set using weaker encryption.

The encryption strength was checked in NIS before and after the passwd change, with:

ypcat passwd | grep <username>

It is clear in the ypcat data that before the change, a very long complex hash was present, and after the change, a rather short hash was present. (Note: In this NIS database, shadow data has been merged into passwd data.)

Resolution

For SLES 12 / SLES 15 :

The pam_unix module (used by default on SLES 12 / SLES 15 systems) which controls the password setting also references the /etc/login.defs file for additional setting on which encryption to use.

Find and set these settings to sha512 (or whatever encryption is desired):

ENCRYPT_METHOD SHA512
ENCRYPT_METHOD_NIS SHA512

For more information, also see "man pam_unix" as well as comments within /etc/login.defs.

For SLES 11:

The pam_unix2 module (used by default on SLES 11 systems) which controls the password setting also references the /etc/default/passwd file for additional setting on which encryption to use.
Find and set these settings to sha512 (or whatever encryption is desired):

CRYPT=sha512
CRYPT_FILES=sha512
CRYPT_YP=sha512

For more information, also see "man pam_unix2" as well as comments within /etc/defaults/passwd.

Cause

The pam_unix module (used by default on SLES 12 / SLES 15 systems) which controls the password setting also references the /etc/login.defs file for additional setting on which encryption to use.

Additional Information

The pam_unix module (used by default on SLES 12 / SLES 15 systems) which controls the password setting also references the /etc/login.defs file for additional setting on which encryption to use.

Disclaimer

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