Netware Super Library/Netware Super Library.iso/app_note/an007b/an007b.txt

Text File | 1991-01-10 | 26KB | 550 lines

An Overview of Virus Prevention Strategies in a NetWare Environment

 Cort Ouderkirk
 Consultant
 Systems Engineering Division

 Drew F. Jackman
 Associate Consultant
 Systems Engineering Division

Abstract:

Computer viruses have been classified as the latest terrorist attack.
Strategies such as the use of detection programs and corporate policies
that deal with this threat are a must. In a NetWare environment; there
are several inherent virus protection facilities, including significant
password restrictions, directory rights, file attributes and supervisor
restrictions. These facilities, combined with good security strategy and
thorough implementation will greatly reduce the odds of a computer virus
infection.

Introduction

With the recent conviction of Robert Morris (1988 Internet Worm), and the
increased number of computer viral infections, network managers have been
forced to confront greater network security issues. This AppNote
addresses issues that relate to the NetWare operating system and virus
infections. These issues include general infection prevention strategies,
built-in NetWare protection, and detection and elimination strategies.

Although much attention has been given to viruses, it is not the intent
of this AppNote to give viruses any more attention than necessary, but we
do want NetWare users to be aware of how they can protect themselves
against undesired attacks.

A virus is a computer program that attaches itself and becomes a parasite
to a computer system. The virus causes the computer system to react in
ways not originally intended. This can range from harmless but annoying
messages displayed on the screen to very destructive programs that attack
computer data.

The most common type of virus attaches itself to .COM and .EXE files or
the boot sector track of a bootable disk. The virus may also try to
infect and invade other parts of the computer system, including other
executable programs and bootable disks. Once a virus enters a system it
can be difficult to determine what damage has been done and how many
programs or data files may be infected.

Although some viruses are difficult to detect, viruses that proceed
undetected may exhibit one or more of the following symptoms.

*    The changing of a volume label, or file size and date

*    An unwarranted number of bad sectors on a disk. Some viruses hide
     themselves in fake bad sectors

*    A floppy disk drive light being on when the default directory is not
     on that drive

*    A major system slow down, but this could also be a hardware problem.

*    The changing of read-only flags to read-write, or printed copies
     with mysterious character changes.

By the time these symptoms are noticed, the damage may already be done.

The best way to deal with a computer virus is to avoid it completely. The
best corrective medicine is prevention. The following sections outline
the access points of possible network infection and the strategies
network managers can use to secure their network against these new
industrial terrorists in the workplace.

Network access points

Diskettes

The first and most common access point is the floppy disk drive. This is
where unsuspecting users can initiate the most harm. Floppy disk drives
include the use of shrink-wrapped software, public domain or shareware
packages, and personal diskettes (user diskettes from home). All of these
diskettes should be checked for viruses before being used.

Even with commercial packages care must be taken to avoid the spread of
viruses. All software on a network should come from reliable dealers or a
reliable source. All software packages should be in the original
packaging. Many software manufacturers are concerned about viruses and
are using the suggestions reproduced in this report.

Public domain and shareware packages also concern network managers. There
are two ways for a manager to confront this type of software. They could
restrict it completely, making a policy that no public domain or
shareware packages be used on the network. But this limits the use of
many good programs. The second possibility is to establish a screening
policy that checks all software coming into a company network. This
policy could include virus protection programs or trying the software on
an isolated machine or network for a period of time. Either of these
policies require that an implementation plan be devised by the manager.
These techniques are also recommended for shrink-wrapped software and
personal diskettes.

Always use working copies of the software. Never use the original
diskettes unless an infection occurs. Keep the original diskettes in a
secure place. Additionally, all originals and working copies (including
boot diskettes) should always be write-protected.

Modem connections

Another access point to monitor is the modem connections on the LAN.
Reliability is a key factor. A reliable bulletin board must be used and
the down-loaded software must be inspected using the same procedure that
is used when other public domain or shareware products come into a
network. A reliable bulletin-board would be one that is concerned about
the spreading of viruses, and has a system for checking the software
placed on it.

Hard disks

When using a system with a hard disk always boot from the hard disk
rather than from a floppy disk. This will help eliminate the chance of
getting a boot sector virus on a workstation. When installing a new hard
disk, always format it before using it. There have been cases where
viruses were found on new hard disks.

Prevention strategies

LAN backups

A reliable LAN backup strategy cannot be overlooked, virus or no virus.
Sooner or later the hardware, software, users or virus infection will
cause the LAN to fail. The robustness of the backup system will determine
how quickly the LAN supervisor will be able to restore the LAN to its
full operation. If the backup storage rotation can be easily followed
back beyond the time of failure, and the restoration procedure is
thorough, a minimal amount of data will be lost. For more information on
the specifics of LAN backup procedures see Network Backup by Paul Turner
and Bob Jones, available through the normal Novell distribution channels.

Diskless workstations

Most viruses enter a computer system through the use of diskettes. One
method of stopping this invasion is to install diskless workstations on
the LAN.

Virus detection programs

There are numerous utilities available for detecting and eliminating
viruses. Some of these programs are terminate and stay resident (TSR)
programs that check all incoming executable programs and stop infected
programs from executing on the local machine. Network versions are
available which are capable of searching a network's virtual drives. Some
of the virus-detection programs also include utilities to disinfect an
infected system.

Users of virus detection programs should know that viruses are extremely
hard to detect, and there is no general virus detection program. All
detection programs only check for known viruses (Burger 1988). This is a
very effective method since most new viruses are just revisions of an
old, previously written virus. However, the probability still exists that
a new virus will not be detected by these programs. Virus detection
programs may slow down the boot-up process and execution times and may
also use some of the system interrupts.

The following is a list of virus products, though it is not exhaustive.

Software package              Company             Phone

Quarantine                    OnDisk Software     [phone]

Anti-Virus Kit                1stAid Software     [phone]

SiteLock                      Brightwork Dev. Inc.[phone]

Viruscan, Scanres, Netscan    McAfee and Assoc.   [phone]

Virus-Pro                     Intl. Security Tech.[phone]

Certus                        Foundation Ware     [phone]

User education

One of the most important strategies of network management is to educate
all the network users about known symptoms and harmful effects of
viruses. Even with all of the above precautionary steps in place, there
is no guarantee that a virus will not infect your network. Viruses will
not go away. But, if users are conscientious about using the access
points, the chances of avoiding a virus infection will increase.

NetWare security facilities

NetWare includes a robust set of security facilities that can prevent
viruses from infecting the network when implemented properly. NetWare
enforces network security, but the system supervisor is responsible for
setting up and maintaining proper security procedures.

An example of this is illustrated by an article written by Barry Gerber,
director of Social Science Computing at the University of California at
Los Angeles. One of the NetWare networks in his computer lab contracted a
virus and he said, -we soon realized that most of the damage had been
done by our staff when they logged in with supervisors' rights from lab
machines in which COMMAND.COM had become infected by students who brought
in their own infected programs." (PC Week April 1990). The following
information will help to avoid problems like this and will strengthen a
NetWare LAN's line of defense.

Password protection

A first line of defense against virus infection of a network is to ensure
that everyone has account restrictions and uses a password. Using a
password prevents unscrupulous users from getting access to the network,
reducing the likelihood of network infection. When users do not have
passwords or enforced account restrictions additional access points are
created for network virus infiltration.

The following are other password precautions:

1)   Require each user to have a unique password.

2)   Require users to change the password periodically.

3)   Make passwords conform to a minimum length standard.

4)   Lock the account if the user fails to log in correctly within a
     maximum number of tries.

These precautions will make a network more secure. If users are required
to change their passwords often and make each new password different from
previous passwords, it will be more difficult for an intruder to break
into the network. Adding an additional character to a password increases
the possible combinations exponentially. Make sure users have passwords
that conform to a minimum length. Locking an account keeps password
breaking programs from repeatedly trying to break in.

Users should also be restricted from including any portion of their
account name or full name in their password. This means that user names
should not be used in any form, either spelled backwards, doubled or run
together. Users should not be allowed to use other personal information
for passwords, such as job title, wife's name, children's names, street
address or other information which may be easily found or guessed.

Disk format

NetWare has added extended security features to the DOS directory
structure and file attributes. Because of these features, the format of
the data that is laid down on the boot track of the NetWare disk is
different from that on DOS disks. With this difference, viruses that
infect the boot track on a DOS machine will not affect a NetWare disk.
Since NetWare is a server operating system and is remote from the
workstations it is harder for boot sector viruses to infect the server.
The virus would have to do its damage before the file server is booted.
As long as the disks used to configure a file server do not become
contaminated, a boot sector virus would not be able to penetrate the file
server boot area.

File attributes

NetWare has added security extensions to file and directory attributes
which make its disk format incompatible with the DOS format. These
security extensions are a part of NetWare which not only help protect the
server from being corrupted, but also protect executable files and data
files from becoming infected by a virus. Security rights control which
directories, subdirectories and files a user can access and what the user
is allowed to do with those directories, subdirectories and files.

File attributes, or flags as they are frequently called, give additional
information about a file other than its name. For example, a file can be
given the attribute of read-only so you cannot accidentally copy over the
file, modify it or delete it. The flags common to both 286-based NetWare
and NetWare 386 that aid in stopping a virus from infecting a file are:

Read-Only      Prevents a file from being written to or modified

Execute-Only   Prevents an executable file from being copied off the
               server

NetWare 386 specific flags include:

Copy Inhibit        Prevents the file from being copied

Delete Inhibit      Prevents the file from being deleted. This flag and
                    the rename inhibit flag are automatically set, when
                    the read-only flag is set

Rename Inhibit Prevents the file from being renamed

The most widely used flag and the best one for preventing a virus from
infecting an executable program is the read-only attribute. Since most
viruses attack executable files, flagging .COM and .EXE files as read-
only will prevent a virus from attaching itself to the file. This
prevention occurs because a user running the program only has read
rights. In order for a virus to attach itself to a program, the infected
user account must have write capabilities. If users have the ability to
write to a program, then the program is not safeguarded and has the
potential to become infected. These file attributes can be assigned with
the FLAG command. The syntax for using the FLAG command is:

FLAG filename attributes

For example, to give the login program the read-only attribute, the
syntax would be:

FLAG login.exe RO

After the read-only attribute has been given, the login program can only
be read and cannot be written to. Viruses that attach to executable
programs cannot attach to programs that are flagged as read-only unless
the user has the modify file attribute right. Typically, the flags on a
system executable file, such as LOGIN.EXE, should only be modifiable by
the system supervisor.

Directory rights

Effective rights are the rights a user can exercise in a given directory.
These are assigned by the system supervisor in the form of trustee
assignments which are given to specific users or groups of users. Trustee
assignments control which directories, subdirectories and files a user or
group can access, and what the user or group can do with them. There are
several rights a supervisor can grant for a directory, including read,
write, search and modify. Once the supervisor grants one or more of these
rights, the user or group may exercise that right in that directory and
its subdirectories.

The directory right of most concern for virus control is the Modify
right. This right allows the user or group to change the file attributes
for files in that directory or its subdirectories. If a user has modify
rights to a directory, a virus has the potential to change an executable
program from read-only to read-write and infect the file. However,
without the modify right in a directory, a virus cannot change a file's
read-only flag in that directory.

For example, if a user runs an infected program at a workstation. The
user's workstation becomes infected. The virus will now try to infect
every program the user runs. If one of those programs happens to be the
LOGIN.EXE program on the file server, the virus will try to infect
LOGIN.EXE even if it is flagged as read-only. If the user has modify
rights to the LOGIN directory, the virus could change the read-only flag
to read-write, and infect the LOGIN utility. If this occurs, everyone who
logs in to the network will become infected. In this way the infection
can spread very rapidly. Once the supervisor becomes infected, nothing on
the network is safe, and every program that is run can become infected.

Therefore, it is vital that only the supervisor have the modify right to
system files. It is also vital that the supervisor take care not to
become infected. Since the login program can cause many users to become
infected quickly, the supervisor may consider taking the command off the
network and putting it on each user's workstation. By doing this, the
spread of the virus would be slowed considerably. However, if the LOGIN
utility is flagged as read-only with only the supervisor having modify
rights, keeping the LOGIN utility on the network should be safe.

Supervisor account restrictions

On a NetWare server the supervisor has ultimate authority and can access
any program or database on the server. Because of this, the damage that
an infected supervisor account can do to the network is significant. To
safeguard against infection, the supervisor account should only be used
when necessary. No user should use the supervisor account as a general
working account but should only use the supervisor account when doing
system work.

To further protect the system, care should be given as to which and how
many users are given the supervisor account password and supervisor
equivalence. Supervisor equivalence can be as dangerous as the supervisor
account itself. The number of people who have the supervisor account
password or supervisor equivalence increases the entry points a virus has
to the network. Users should not be limited in the work they do, but most
do not need supervisor authority.

Another precaution is to limit the workstations the supervisor account
can log in from. By doing this, the supervisor account cannot be logged
into inadvertently on an infected station. This could happen if a user
brings in an infected program to run on a workstation. After a while the
user notices that the system isn't working correctly and calls the
network supervisor. The supervisor then logs in using the supervisor
account. When this happens the supervisor becomes infected and will
infect everything accessed. Every program the supervisor runs can become
infected and possibly data files will become contaminated. However, if
the number of workstations the supervisor can log in to is limited, this
mistake will not be made. We suggested that the supervisor account be
active for at least two workstations. This will allow the supervisor to
access the network if one of those workstations fail.

Another way to enhance system security and minimize the entry points a
virus has to the network is to limit the number of simultaneous
connections a supervisor account may have. Restrict this to one, so the
supervisor may only log in to one workstation at a time.

Elimination

If a virus infects a network, the manager's actions in treating the virus
are critical. This section suggests some ways to eliminate a virus that
has infected a LAN. These steps alleviate some of the panic that a virus
infection causes. This is a blanket repair approach taken from Computer
Viruses, A High-Tech Disease, by Ralf Burger, and will not fit all
network situations.

1)   Turn off the system (including workstations) to prevent further
spread of the virus, and to destroy any memory resident viruses. Do not
warm boot the system computers, some viruses can survive a CTRL-ALT-DEL.

2)   Disconnect all data transfer lines from the system. This isolates
the system from infecting other systems and keeps infection from
recurring while the system is being restored.

3)   Write-protect all media that has not previously been protected. This
includes all notched diskettes, and all drives and magnetic tapes that
have write-protect switches.

4)   Use the original version of the operating system to reboot the
system. It is possible that a virus has infected the backup or working
copies.

5)   Save the system data and programs on new media. These can be used to
support damage claims, and may also give an idea where the virus
originally infected the system.

6)   Format old media, a virus cannot survive a media format.

7)   Use the original versions of all other software to restore system
packages. Make sure they are still write protected.

8)   After the restoration, check all data for dependability. When proper
order has been restored, the data can be used.

9)   If data consistency cannot be guaranteed, then use a backup copy
which will guarantee consistency.

10)  Install detection software that will check the system in the future.
If unusual behavior continues, then contact a virus consulting firm for
help.

Another effective method for removing a virus is the use of commercial
disinfecting programs. Many of these programs can clean up infected
systems by removing just the virus code. Others clean up the system by
removing the infected software completely. Familiarity with a particular
package will be helpful in case of infection.

Conclusion

Knowing how viruses work, how they spread and the damage they can do
allows network managers to better secure their systems. By using good
management techniques in conjunction with NetWare security, a virus can
be prevented from entering and spreading throughout a network. As
networks continue to grow and involve all aspects of company's business,
the access points to a network increase. Therefore, to safeguard networks
and data on those networks, network managers must be willing to implement
these techniques before a virus enters their system.

Bibliography

Baker, Virginia E. Infectious Diseases. LAN Times (Dec. 1989).

Burger, Ralf. Computer Viruses: a High Tech Disease. Abacus. (Second ed.
1988).

De Martin, Lawrence. How to Protect PCs from Viruses and Anti-Viral
Software. Connect. (Summer 1989).

Gerber, Barry. Sometimes -Abort, Retry" Means -Network Virus". PC Week.
(April 1990).

Hoffman, Patricia. Virus Information Summary List. (Feb. 1990).

Neff, Ken. Fifteen Preventive Measures. LAN Times. (Dec. 1989).


Cumulative Index

NetWare Application Notes

Novell Systems Engineering Division
Released Application Notes

To request additional NetWare Application Notes, contact your Authorized
NetWare Reseller, your Novell Field Sales Representative or Systems
Engineer.

Application
Note
Edition        Part Number              Title

June 1990      119-000010-001           286-Based NetWare v2.1x File
                                        Service Processes: The Final Word

                                        Novell NetWare and AT&T
                                        Integration

                                        NetWare Internal and External
                                        Bridge Performance Benchmarking

July 1990      164-000011-001           NetWare 386 System Messages:
                                        Disk, Memory and Accounting

                                        An Overview of Virus Prevention
                                        Strategies in a NetWare
                                        Environment


Compaq Application Notes (NetWare-related only)

Compaq Systems Engineering Department Released Application Notes

To request additional Compaq Application Notes, contact your Authorized
COMPAQ Computer Dealer or your Compaq Field Sales Representative.

Application
Note           Document
Number         Control Number           Title
-------------------------------------------------------------------------
1989

AN89-0002      191A/0489                Influence of Ethernet NICs on LAN
                                        Server Benchmarks

AN89-0003      192A/0489                DCA IRMALAN Gateways on Novell
                                        Ethernet/Token-Ring LAN

AN89-0008      114A/0689                Installation of Gupta
                                        Technologies SQLBASE in
                                        Single and Bridged Token-
                                        Ring/Ethernet LAN
                                        Environments

1990

AN90-0002      122A/0290                Installation of Novell NetWare
                                        386 on the COMPAQ SYSTEMPRO

AN90-0003      223A/0390                RAM Cram Relief Using Expanded
                                        Memory Management Products

AN90-0004      224A/0390                Configuration of a Dataproducts
                                        High-Speed Line Printer with
                                        COMPAQ Platforms

AN90-006       269A/0390                Novell 286-Based NetWare
                                        Installation on the COMPAQ
                                        SYSTEMPRO

AN90-0008      208A/0590                Use of COMPAQ-Product RAM Greater
                                        Than 16MB With Novell NetWare 386
                                        v3.0

AN90-0009      209A/0590                Novell 286-Based NetWare to UNIX
                                        Connectivity Using Racal-Interlan
                                        TCP Gateway for Novell NetWare

AN90-0011      196A/0790                Emeral Tape Backup System for
                                        Novell 286-Based NetWare