This bug has been copied from bug #841070 and has been proposed to be backported to 5.8 z-stream (EUS).
Since the problem described in this bug report should be resolved in a recent advisory, it has been closed with a resolution of ERRATA. For information on the advisory, and where to find the updated files, follow the link below. If the solution does not work for you, open a new bug report. http://rhn.redhat.com/errata/RHSA-2012-1149.html
This fix leaves /etc/nsswitch.conf as permissions 0600 (because the postinstall uses mktemp). nsswitch.conf needs to be 0644 instead of 0600.
see CentOS bug #5883: http://bugs.centos.org/view.php?id=5883
Technical note added. If any revisions are required, please edit the "Technical Notes" field accordingly. All revisions will be proofread by the Engineering Content Services team. New Contents: Updating the sudo package resulted in the "sudoers" line in "/etc/nsswitch.conf" being removed. This update corrects the bug in the sudo package's post-uninstall script that caused this issue.