Password File Access ControlOne way

Password File Access Control
One way to thwart a password attack is to deny the opponent access to the password
file. If the hashed password portion of the file is accessible only by a privileged user,
then the opponent cannot read it without already knowing the password of a privileged
user. Often, the hashed passwords are kept in a separate file from the user
IDs, referred to as a shadow password file . Special attention is paid to making the
shadow password file protected from unauthorized access. Although password file
protection is certainly worthwhile, there remain vulnerabilities:
• Many systems, including most UNIX systems, are susceptible to unanticipated
break-ins. A hacker may be able to exploit a software vulnerability in the
operating system to bypass the access control system long enough to extract
the password file. Alternatively, the hacker may find a weakness in the file
system or database management system that allows access to the file.
• An accident of protection might render the password file readable, thus compromising
all the accounts.
• Some of the users have accounts on other machines in other protection
domains, and they use the same password. Thus, if the passwords could
be read by anyone on one machine, a machine in another location might be
compromised.
• A lack of or weakness in physical security may provide opportunities for a
hacker. Sometimes there is a backup to the password file on an emergency
repair disk or archival disk. Access to this backup enables the attacker to read
the password file. Alternatively, a user may boot from a disk running another
operating system such as Linux and access the file from this OS.
• Instead of capturing the system password file, another approach to collecting
user IDs and passwords is through sniffing network traffic.