Security models have been developed for each of the network types
at NRL. The network specific models are intended to provide
system
managers with the basic controls needed to initially secure and
then continue to secure their networks. These models are
supplied
to managers as necessary by the IS Security Office. Along with
these recommended controls, the following information is
provided.
Sub-networks
If a user has accounts on more than one sub-network,
different
passwords should be used on each sub-network. If one computer on
a sub-network is compromised, other computers are still
protected.
Home Directory Permissions
In UNIX, a user's home directory should not be world
writable.
A world writable directory allows anyone to substitute one of
their
files for one of the users. For instance, an unauthorized user
might replace a user's login file with one that does undesired
things. To set the directory permission use:xxxxxxxxxxxxxxxxxxxx
X-windows
When running X windows, only grant access to the display to
clients from specified machines. Use xhost + machine name
instead
of xhost +. This will retard others from running clients on the
display without your permissions
Leaving the Console Unattended
If a user has to leave the terminal, he/she should either use
a screen locker program to prevent others from using the account,
or logout.
Unattended Telnet Sessions
Don't leave telnet session unattended for long periods of
time,
such as overnight. It is possible to break into a telnet session
and assume the identity of the user who originated the session.
Many screen lockers, such as xlock, don't prevent others from
accessing your machine over the network. They only lock the
keyboard. Logout instead of using a screen locker over night and
over weekends.
Check Last Time You Logged In
The computer should be configured to print out the user's
last
time and location each time the user is granted access. Users
should verify that the last session logged in was really them.
They should also get in the habit of looking at the last log
to
see if there are any irregularities. In UNIX this can be done
with
the command : last .
Strange Files
Keep an eye out for files in directories that don't belong.
With UNIX, intruders like to hide files by naming them something
that starts with a period (.) because these files are not listed
when the standard Is command is given. Get in the habit of
checking for these types of files.
Finding an Unauthorized Access
If a user discovers an unauthorized access, or suspects one
has
happened, he/she should contact the system administrator
immediately! Contact the system administrator either with a
personal visit, or a phone call. Sending email to the system
administrator runs the risk of alerting the unauthorized user
that
he/she has been found when the unauthorized user intercepts the
mail message.
If unauthorized access is discovered, the following platform
specification documents should be supplied by the user to the IS
Security Office:
1. Specific security models
2. Specific testing procedures
3. Specific investigation procedures
Backup Data
Each user should backup files regularly. A user may wish to
backup
data every day, or at the very least every week. Backups should
be
done either to tape or to the lab wide archives. Many users
choose
to keep the backup tape in a separate physical location from the
computer. If a fire, flood, or other catastrophe happens to the
computer, the tape doesn't fall prey to the same catastrophe.
The
system administrator should back up system and user files
regularly, but if a problem does happen, it is the user that
loses
all his/her hard work, so backing up is always a good idea.