Information
The /etc/shadow file is used to store the information about user accounts that is critical to the security of those accounts, such as the hashed password and other security information.
If attackers can gain read access to the /etc/shadow file, they can easily run a password cracking program against the hashed password to break it. Other security information that is stored in the /etc/shadow file (such as expiration) could also be useful to subvert the user accounts.
Solution
Run the one of the following chown commands as appropriate and the chmod to set permissions on /etc/shadow :
# chown root:root /etc/shadow
# chown root:shadow /etc/shadow
# chmod o-rwx,g-wx /etc/shadow