Did somebody chown the sudoers files ? Did they change the ownership of any other system files ?
Originally Posted by doctorproctor
I would be concerned what other system files may have changed.
You may need to boot into a LiveCD/USB to change it back after mounting it .
Make sure the permissions are 440
chown 0:0 <mount_point>/etc/sudoers
As i said before though, have the permissions of any other system file changed ?
chmod 440 <mount_point>/etc/sudoers
You need to find out how this happened.
Out of interest which group is 113 ?
grep 113 /etc/group