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RFC2504 - Users Security Handbook

王朝other·作者佚名  2008-05-31
窄屏简体版  字體: |||超大  

Network Working Group E. Guttman

Request for Comments: 2504 Sun Microsystems

FYI: 34 L. Leong

Category: Informational COLT Internet

G. Malkin

Bay Networks

February 1999

Users' Security Handbook

Status of this Memo

This memo provides information for the Internet community. It does

not specify an Internet standard of any kind. Distribution of this

memo is unlimited.

Copyright Notice

Copyright (C) The Internet Society (1999). All Rights Reserved.

Abstract

The Users' Security Handbook is the companion to the Site Security

Handbook (SSH). It is intended to provide users with the information

they need to help keep their networks and systems secure.

Table of Contents

Part One: IntrodUCtion . . . . . . . . . . . . . . . . . . . . 2

1. READ.ME . . . . . . . . . . . . . . . . . . . . . . . . . 2

2. The Wires have Ears . . . . . . . . . . . . . . . . . . . 3

Part Two: End-users in a centrally-administered network . . . 4

3. Watch Out! . . . . . . . . . . . . . . . . . . . . . . . 4

3.1. The Dangers of Downloading . . . . . . . . . . . . . . 4

3.2. Don't Get Caught in the Web . . . . . . . . . . . . . . 5

3.3. Email Pitfalls . . . . . . . . . . . . . . . . . . . . 6

3.4. PassWords . . . . . . . . . . . . . . . . . . . . . . . 7

3.5. Viruses and Other Illnesses . . . . . . . . . . . . . . 7

3.6. Modems . . . . . . . . . . . . . . . . . . . . . . . . 8

3.7. Don't Leave Me... . . . . . . . . . . . . . . . . . . . 9

3.8. File Protections . . . . . . . . . . . . . . . . . . . 9

3.9. Encrypt Everything . . . . . . . . . . . . . . . . . . 10

3.10. Shred Everything Else . . . . . . . . . . . . . . . . . 10

3.11. What Program is This, Anyway? . . . . . . . . . . . . . 11

4. Paranoia is Good . . . . . . . . . . . . . . . . . . . . 11

Part Three: End-users self administering a networked computer 14

5. Make Your Own Security Policy . . . . . . . . . . . . . . 14

6. Bad Things Happen . . . . . . . . . . . . . . . . . . . . 15

6.1. How to Prepare for the Worst in Advance . . . . . . . . 15

6.2. What To Do if You Suspect Trouble . . . . . . . . . . . 16

6.3. Email . . . . . . . . . . . . . . . . . . . . . . . . . 17

7. Home Alone . . . . . . . . . . . . . . . . . . . . . . . 17

7.1. Beware of Daemons . . . . . . . . . . . . . . . . . . . 17

7.2. Going Places . . . . . . . . . . . . . . . . . . . . . 19

7.3. Secure It! . . . . . . . . . . . . . . . . . . . . . . 20

8. A Final Note . . . . . . . . . . . . . . . . . . . . . . 20

Appendix: Glossary of Security Terms . . . . . . . . . . . . . 21

Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 31

References . . . . . . . . . . . . . . . . . . . . . . . . . . 31

Security Considerations . . . . . . . . . . . . . . . . . . . 32

Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 32

Full Copyright Statement . . . . . . . . . . . . . . . . . . . 33

Part One: Introduction

This document provides guidance to the end-users of computer systems

and networks about what they can do to keep their data and

communication private, and their systems and networks secure. Part

Two of this document concerns "corporate users" in small, medium and

large corporate and campus sites. Part Three of the document

addresses users who administer their own computers, such as home

users.

System and network administrators may wish to use this document as

the foundation of a site-specific users' security guide; however,

they should consult the Site Security Handbook first [RFC2196].

A glossary of terms is included in an appendix at the end of this

document, introducing computer network security notions to those not

familiar with them.

1. READ.ME

Before getting connected to the Internet or any other public network,

you should oBTain the security policy of the site that you intend to

use as your Access provider, and read it. A security policy is a

formal statement of the rules by which users who are given access to

a site's technology and information assets must abide. As a user,

you are obliged to follow the policy created by the decision makers

and administrators at your site.

A security policy exists to protect a site's hardware, software and

data. It eXPlains what the security goals of the site are, what

users can and cannot do, what to do and who to contact when problems

arise, and generally informs users what the "rules of the game" are.

2. The Wires have Ears

It is a lot easier to eavesdrop on communications over data networks

than to tap a telephone conversation. Any link between computers may

potentially be insecure, as can any of the computers through which

data flows. All information passing over networks may be

eavesdropped on, even if you think "No one will care about this..."

Information passing over a network may be read not only by the

intended audience but can be read by others as well. This can happen

to personal Email and sensitive information that is accessed via file

transfer or the Web. Please refer to the "Don't Get Caught in the

Web" and "Email Pitfalls" sections for specific information on

protecting your privacy.

As a user, your utmost concerns should, firstly, be to protect

yourself against misuse of your computer account(s) and secondly, to

protect your privacy.

Unless precautions are taken, every time you log in over a network,

to any network service, your password or confidential information may

be stolen. It may then be used to gain illicit access to systems you

have access to. In some cases, the consequences are obvious: If

someone gains access to your bank account, you might find yourself

losing some cash, quickly. What is not so obvious is that services

which are not financial in nature may also be abused in rather costly

ways. You may be held responsible if your account is misused by

someone else!

Many network services involve remote log in. A user is prompted for

his or her account ID (ie. user name) and password. If this

information is sent through the network without encryption, the

message can be intercepted and read by others. This is not really an

issue when you are logging in to a "dial-in" service where you make a

connection via telephone and log in, say to an online service

provider, as telephone lines are more difficult to eavesdrop on than

Internet communications.

The risk is there when you are using programs to log in over a

network. Many popular programs used to log in to services or to

transfer files (such as telnet and FTP, respectively) send your user

name and password and then your data over the network without

encrypting them.

The precaution commonly taken against password eavesdropping by

larger institutions, such as corporations, is to use one-time

password systems.

Until recently, it has been far too complicated and expensive for

home systems and small businesses to employ secure log in systems.

However, an increasing number of products enable this to be done

without fancy hardware, using cryptographic techniques. An example

of such a technique is Secure Shell [SSH], which is both freely and

commercially available for a variety of platforms. Many products

(including SSH-based ones) also allow data to be encrypted before it

is passed over the network.

Part Two: End-users in a centrally-administered network

The following rules of thumb provide a summary of the most important

pieces of advice discussed in Part Two of this document:

- Know who your security point-of-contact is.

- Keep passwords secret at all times.

- Use a password-locked screensaver or log out when you leave your

desk.

- Don't let simply anyone have physical access to your computer or

your network.

- Be aware what software you run and very wary of software of

unknown origin. Think hard before you execute downloaded

software.

- Do not panic. Consult your security point-of-contact, if

possible, before spreading alarm.

- Report security problems as soon as possible to your security

point-of-contact.

3. Watch Out!

3.1. The Dangers of Downloading

An ever expanding wealth of free software has become available on the

Internet. While this exciting development is one of the most

attractive ASPects of using public networks, you should also exercise

caution. Some files may be dangerous. Downloading poses the single

greatest risk.

Be careful to store all downloaded files so that you will remember

their (possibly dubious) origin. Do not, for example, mistake a

downloaded program for another program just because they have the

same name. This is a common tactic to fool users into activating

programs they believe to be familiar but could, in fact, be

dangerous.

Programs can use the network without making you aware of it. One

thing to keep in mind is that if a computer is connected, any program

has the capability of using the network, with or without informing

you. Say, for example:

You download a game program from an anonymous FTP server. This

appears to be a shoot-em-up game, but unbeknownst to you, it

transfers all your files, one by one, over the Internet to a

cracker's machine!

Many corporate environments explicitly prohibit the downloading and

running of software from the Internet.

3.2. Don't Get Caught in the Web

The greatest risk when web browsing is downloading files. Web

browsers allow any file to be retrieved from the Internet. See "The

Dangers of Downloading".

Web browsers are downloading files even when it is not entirely

obvious. Thus, the risk posed by downloading files may be present

even if you do not actively go out and retrieve files overtly. Any

file which you have loaded over the network should be considered

possibly dangerous (even files in the web browser's cache). Do not

execute them by accident, as they may be malicious programs.

(Remember, programs are files, too. You may believe you have

downloaded a text file, when in fact it is a Trojan Horse program,

script, etc.)

Web browsers may download and execute programs on your behalf, either

automatically or after manual intervention. You may disable these

features. If you leave them enabled, be sure that you understand the

consequences. You should read the security guide which accompanies

your web browser as well as the security policy of your company. You

should be aware that downloaded programs may be risky to execute on

your machine. See "What program is this, anyway?".

Web pages often include forms. Be aware that, as with Email, data

sent from a web browser to a web server is not secure. Several

mechanisms have been created to prevent this, most notably Secure

Sockets Layer [SSL]. This facility has been built into many web

browsers. It encrypts data sent between the user's web browser and

the web server so no one along the way can read it.

It is possible that a web page will appear to be genuine, but is, in

fact, a forgery. It is easy to copy the appearance of a genuine web

page and possible to subvert the network protocols which contact the

desired web server, to misdirect a web browser to an imposter.

That threat may be guarded against using SSL to verify if a web page

is genuine. When a 'secure' page has been downloaded, the web

browser's 'lock' or 'key' will indicate so. It is good to

double-check this: View the 'certificate' associated with the web

page you have accessed. Each web browser has a different way to do

this. The certificate will list the certificate's owner and who

issued it. If these look trustworthy, you are probably OK.

3.3 Email Pitfalls

All the normal concerns apply to messages received via Email that you

could receive any other way. For example, the sender may not be who

he or she claims to be. If Email security software is not used, it

is very difficult to determine for sure who sent a message. This

means that Email itself is a not a suitable way to conduct many types

of business. It is very easy to forge an Email message to make it

appear to have come from anyone.

Another security issue you should consider when using Email is

privacy. Email passes through the Internet from computer to

computer. As the message moves between computers, and indeed as it

sits in a user's mailbox waiting to be read, it is potentially

visible to others. For this reason, it is wise to think twice before

sending confidential or extremely personal information via Email.

You should never send credit card numbers and other sensitive data

via unprotected Email. Please refer to "The Wires Have Ears".

To cope with this problem, there are privacy programs available, some

of which are integrated into Email packages.

One service many Email users like to use is Email forwarding. This

should be used very cautiously. Imagine the following scenario:

A user has an account with a private Internet Service Provider and

wishes to receive all her Email there. She sets it up so that her

Email at work is forwarded to her private address. All the Email

she would receive at work then moves across the Internet until it

reaches her private account. All along the way, the Email is

vulnerable to being read. A sensitive Email message sent to her

at work could be read by a network snoop at any of the many stops

along the way the Email takes.

Note that Email sent or received at work may not be private. Check

with your employer, as employers may (in some instances) legally both

read your Email and make use of it. The legal status of Email

depends on the privacy of information laws in force in each country.

Many mail programs allow files to be included in Email messages. The

files which come by Email are files like any other. Any way in which

a file can find its way onto a computer is possibly dangerous. If

the attached file is merely a text message, fine. But it may be more

than a text message. If the attached file is itself a program or an

executable script, extreme caution should be applied before running

it. See the section entitled "The Dangers of Downloading".

3.4 Passwords

Passwords may be easily guessed by an intruder unless precautions are

taken. Your password should contain a mixture of numbers, upper and

lower case letters, and punctuation. Avoid all real words in any

language, or combinations of words, license plate numbers, names and

so on. The best password is a made-up sequence (e.g., an acronym

from a phrase you won't forget), such as "2B*Rnot2B" (but don't use

this password!).

Resist the temptation to write your password down. If you do, keep

it with you until you remember it, then shred it! NEVER leave a

password taped onto a terminal or written on a whiteboard. You

wouldn't write your PIN code on your automated teller machine (ATM)

card, would you? You should have different passwords for different

accounts, but not so many passwords that you can't remember them.

You should change your passwords periodically.

You should also NEVER save passwords in scripts or login procedures

as these could be used by anyone who has access to your machine.

Be certain that you are really logging into your system. Just

because a login prompt appears and asks you for your password does

not mean you should enter it. Avoid unusual login prompts and

immediately report them to your security point-of-contact. If you

notice anything strange upon logging in, change your password.

Unless precautions have been taken to encrypt your password when it

is sent over the network, you should, if possible, use "one-time

passwords" whenever you log in to a system over a network. (Some

applications take care of that for you.) See "The Wires Have Ears"

for more information on the risks associated with logging in over a

network.

3.5 Viruses and Other Illnesses

Viruses are essentially unwanted pieces of software that find their

way onto a computer. What the virus may do once it has entered its

host, depends on several factors: What has the virus been programmed

to do? What part of the computer system has the virus attacked?

Some viruses are 'time bombs' which activate only when given a

particular condition, such as reaching a certain date. Others remain

latent in the system until a particular afflicted program is

activated. There are still others which are continually active,

exploiting every opportunity to do mischief. A subtle virus may

simply modify a system's configuration, then hide.

Be cautious about what software you install on your system. Use

software from "trusted sources", if possible. Check your site policy

before installing any software: Some sites only allow administrators

to install software to avoid security and system maintenance

problems.

Centrally-administered sites have their own policy and tools for

dealing with the threat of viruses. Consult your site policy or find

out from your systems administrator what the correct procedures are

to stay virus free.

You should report it if a virus detection tool indicates that your

system has a problem. You should notify your site's systems

administrators as well as the person you believe passed the virus to

you. It is important to remain calm. Virus scares may cause more

delay and confusion than an actual virus outbreak. Before announcing

the virus widely, make sure you verify its presence using a virus

detection tool, if possible, with the assistance of

technically-competent personnel.

Trojan Horse programs and worms are often categorized with viruses.

Trojan Horse programs are dealt with in the "What Program is This,

Anyway?" section. For the purposes of this section, worms should be

considered a type of virus.

3.6 Modems

You should be careful when attaching anything to your computer, and

especially any equipment which allows data to flow. You should get

permission before you connect anything to your computer in a

centrally-administered computing environment.

Modems present a special security risk. Many networks are protected

by a set of precautions designed to prevent a frontal assault from

public networks. If your computer is attached to such a network, you

must exercise care when also using a modem. It is quite possible to

use the modem to connect to a remote network while *still* being

connected to the 'secure' net. Your computer can now act as a hole

in your network's defenses. Unauthorized users may be able to get

onto your organization's network through your computer!

Be sure you know what you are doing if you leave a modem on and set

up your computer to allow remote computers to dial in. Be sure you

use all available security features correctly. Many modems answer

calls by default. You should turn auto-answer off unless you are

prepared to have your computer respond to callers. Some 'remote

access' software requires this. Be sure to turn on all the security

features of your 'remote access' software before allowing your

computer to be accessed by phone.

Note that having an unlisted number will not protect you from someone

breaking into your computer via a phone line. It is very easy to

probe many phone lines to detect modems and then launch attacks.

3.7 Don't Leave Me...

Do not leave a terminal or computer logged in and walk away. Use

password-locked screensavers whenever possible. These can be set up

so that they activate after the computer has been idle for a while.

Sinister as it may seem, someone coming around to erase your work is

not uncommon. If you remained logged in, anyone can come by and

perform mischief for which you may be held accountable. For example,

imagine the trouble you could be in for if nasty Email were sent to

the president of your company in your name, or your account were used

to transfer illegal pornography.

Anyone who can gain physical access to your computer can almost

certainly break into it. Therefore, be cautious regarding who you

allow access to your machine. If physically securing your machine is

not possible, it is wise to encrypt your data files kept on your

local hard disk. If possible, it is also wise to lock the door to

one's Office where the computer is stored.

3.8 File Protections

Data files and Directories on shared systems or networked file

systems require care and maintenance. There are two categories of

such systems:

- Files to share

Shared files may be visible to everyone or to a restricted group

of other users. Each system has a different way of specifying

this. Learn how to control sharing permissions of files and

implement such control without fail.

- Protected files

These include files that only you should have access to, but

which are also available to anyone with system administrator

privileges. An example of this are files associated with the

delivery of Email. You don't want other users to read your Email,

so make sure such files have all the necessary file permissions

set accordingly.

3.9 Encrypt Everything

Additionally, there are files that are private. You may have files

which you do not wish anyone else to have access to. In this case,

it is prudent to encrypt the file. This way, even if your network is

broken into or the systems administrator turns into Mr. Hyde, your

confidential information will not be available. Encryption is also

very important if you share a computer. For example, a home computer

may be shared by room mates who are friends but prefer to keep their

Email and financial information private. Encryption allows for

shared yet private usage.

Before you encrypt files, you should check your site's security

policy. Some employers and countries expressly forbid or restrict

the storing and/or transferring of encrypted files.

Be careful with the passwords or keys you use to encrypt files.

Locking them away safely not only helps to keep them from prying eyes

but it will help you keep them secure too; for if you lose them, you

will lose your ability to decrypt your data as well! It may be wise

to save more than one copy. This may even be required, if your

company has a key escrow policy, for example. This protects against

the possibility that the only person knowing a pass phrase may leave

the company or be struck by lightning.

Whilst encryption programs are readily available, it should be noted

that the quality can vary widely. PGP (which stands for "Pretty Good

Privacy") for example, offers a strong encryption capability. Many

common software applications include the capability to encrypt data.

The encryption facilities in these are typically very weak.

You should not be intimidated by encryption software. Easy-to-use

software is being made available.

3.10 Shred Everything Else

You would be surprised what gets thrown away into the waste-paper

basket: notes from meetings, old schedules, internal phone lists,

computer program listings, correspondence with customers and even

market analyses. All of these would be very valuable to competitors,

recruiters and even an overzealous (hungry?) journalist looking for a

scoop. The threat of dumpster diving is real - take it seriously!

Shred all potentially useful documents before discarding them.

You should also be aware that deleting a file does not erase it in

many cases. The only way to be sure that an old hard disk does not

contain valuable data may be to reformat it.

3.11 What Program is This, Anyway?

Programs have become much more complex in recent years. They are

often extensible in ways which may be dangerous. These extensions

make applications more flexible, powerful and customizable. They

also open the end-user up to all sorts of risks.

- A program may have "plug-in" modules. You should not trust the

plug-ins simply because you are used to trusting the programs

they plug into. For example: Some web pages suggest that the

user download a plug-in to view or use some portion of the web

page's content. Consider: What is this plug-in? Who wrote it?

Is it safe to include it in your web browser?

- Some files are "compound documents". This means that instead of

using one single program, it will be necessary to run several

programs in order to view or edit a document. Again, be careful

of downloading application components. Just because they

integrate with products which are well-known does not mean that

they can be trusted. Say, you receive an Email message which can

only be read if you download a special component. This component

could be a nasty program which wipes out your hard drive!

- Some programs are downloaded automatically when accessing web

pages. While there are some safeguards to make sure that these

programs may be used safely, there have been security flaws

discovered in the past. For this reason, some centrally-

administered sites require that certain web browser capabilities

be turned off.

4. Paranoia is Good

Many people do not realize it, but social engineering is a tool which

many intruders use to gain access to computer systems. The general

impression that people have of computer break-ins is that they are

the result of technical flaws in computer systems which the intruders

have exploited. People also tend to think that break-ins are purely

technical. However, the truth is that social engineering plays a big

part in helping an attacker slip through security barriers. This

often proves to be an easy stepping-stone onto the protected system

if the attacker has no authorized access to the system at all.

Social engineering may be defined, in this context, as the act of

gaining the trust of legitimate computer users to the point where

they reveal system secrets or help someone, unintentionally, to gain

unauthorized access to their system(s). Using social engineering, an

attacker may gain valuable information and/or assistance that could

help break through security barriers with ease. Skillful social

engineers can appear to be genuine but are really full of deceit.

Most of the time, attackers using social enginering work via

telephone. This not only provides a shield for the attacker by

protecting his or her identity, it also makes the job easier because

the attacker can claim to be a particular someone with more chances

of getting away with it.

There are several types of social engineering. Here are a few

examples of the more commonly-used ones:

- An attacker may pretend to be a legitimate end-user who is new to

the system or is simply not very good with computers. This

attacker may approach systems administrators and other end-users

for help. This "user" may have lost his password, or simply can't

get logged into the system and needs to access the system

urgently. Attackers have also been known to identify themselves

as some VIP in the company, screaming at administrators to get

what they want. In such cases, the administrator (or it could be

an end-user) may feel threatened by the caller's authority and

give in to the demands.

- Attackers who operate via telephone calls may never even have seen

the screen display on your system before. In such cases, the

trick attackers use is to make details vague, and get the user to

reveal more information on the system. The attacker may sound

really lost so as to make the user feel that he is helping a

damsel in distress. Often, this makes people go out their way to

help. The user may then reveal secrets when he is off-guard.

- An attacker may also take advantage of system problems that have

come to his attention. Offering help to a user is an effective

way to gain the user's trust. A user who is frustrated with

problems he is facing will be more than happy when someone comes

to offer some help. The attacker may come disguised as the

systems administrator or maintenance technician. This attacker

will often gain valuable information because the user thinks that

it is alright to reveal secrets to technicians. Site visits may

pose a greater risk to the attacker as he may not be able to make

an easy and quick get-away, but the risk may bring fruitful

returns if the attacker is allowed direct access to the system by

the naive user.

- Sometimes, attackers can gain access into a system without prior

knowledge of any system secret nor terminal access. In the same way

that one should not carry someone else's bags through Customs, no user

should key in commands on someone's behalf. Beware of attackers who

use users as their own remotely-controlled fingers to type commands on

the user's keyboard that the user does not understand, commands which

may harm the system. These attackers will exploit system software

bugs and loopholes even without direct access to the system. The

commands keyed in by the end-user may bring harm to the system, open

his own account up for access to the attacker or create a hole to

allow the attacker entry (at some later time) into the system. If you

are not sure of the commands you have been asked to key in, do not

simply follow instructions. You never know what and where these could

lead to...

To guard against becoming a victim of social engineering, one

important thing to remember is that passwords are secret. A password

for your personal account should be known ONLY to you. The systems

administrators who need to do something to your account will not

require your password. As administrators, the privileges they have

will allow them to carry out work on your account without the need

for you to reveal your password. An administrator should not have to

ask you for your password.

Users should guard the use of their accounts, and keep them for their

own use. Accounts should not be shared, not even temporarily with

systems administrators or systems maintenance techinicians. Most

maintenance work will require special privileges which end-users are

not given. Systems administrators will have their own accounts to

work with and will not need to access computer systems via an

end-user's account.

Systems maintenance technicians who come on site should be

accompanied by the local site administrator (who should be known to

you). If the site administrator is not familiar to you, or if the

technician comes alone, it is wise to give a call to your known site

administrator to check if the technician should be there. Yet, many

people will not do this because it makes them look paranoid and it is

embarrassing to show that they have no, or little trust in these

visitors.

Unless you are very sure that the person you are speaking to is who he

or she claims to be, no secret information should ever be revealed to

such people. Sometimes, attackers may even be good enough to make

themselves sound like someone whose voice you know over the phone. It

is always good to double check the identity of the person. If you are

unable to do so, the wisest thing to do is not to reveal any secrets.

If you are a systems administrator, there should be security

procedures for assignment and reassignment of passwords to users, and

you should follow such procedures. If you are an end-user, there

should not be any need for you to have to reveal system secrets to

anyone else. Some companies assign a common account to multiple

users. If you happen to be in such a group, make sure you know

everyone in that group so you can tell if someone who claims to be in

the group is genuine.

Part Three: End-users self administering a networked computer

The home user or the user who administers his own network has many of

the same concerns as a centrally-administered user. The following is

a summary of additional advice given in Part Three:

- Read manuals to learn how to turn on security features, then turn

them on.

- Consider how private your data and Email need to be. Have you

invested in privacy software and learned how to use it yet?

- Prepare for the worst in advance.

- Keep yourself informed about what the newest threats are.

5. Make Your Own Security Policy

You should decide ahead of time what risks are acceptable and then

stick to this decision. It is also wise to review your decision at

regular intervals and whenever the need to do so arises. It may be

wise to simply avoid downloading any software from the network which

comes from an unknown source to a computer storing business records,

other valuable data and data which is potentially damaging if the

information was lost or stolen.

If the system has a mixed purpose, say recreation, correspondence

and some home accounting, perhaps you will hazard some downloading of

software. You unavoidably take some risk of acquiring stuff

which is not exactly what it seems to be.

It may be worthwhile installing privacy software on a computer if it

is shared by multiple users. That way, a friend of a room mate won't

have access to your private data, and so on.

6. Bad Things Happen

If you notice that your files have been modified or ascertain somehow

that your account has been used without your consent, you should

inform your security point-of-contact immediately. When you do

not know who your security point-of-contact is, try calling

your Internet service provider's help desk as a first step.

6.1 How to Prepare for the Worst in Advance

- Read all user documentation carefully. Make sure that it is clear

when services are being run on your computer. If network services

are activated, make sure they are properly configured (set all

permissions so as to prevent anonymous or guest logins, and so

on). Increasingly, many programs have networking capabilities

built in to them. Learn how to properly configure and safely use

these features.

- Back up user data. This is always important. Backups are

normally thought of as a way of ensuring you will not lose your

work if a hard disk fails or if you make a mistake and delete a

file. Backing up is also critical to insure that data cannot be

lost due to a computer security incident. One of the most vicious

and unfortunately common threats posed by computer viruses and

Trojan Horse programs is erasing a computer's hard disk.

- Obtain virus checking software or security auditing tools. Learn

how to use them and install them before connecting to a public

network. Many security tools require that they be run on a

"clean" system, so that comparisons can be made between the

present and pristine states. Thus, it is necessary for some work

to be done ahead of time.

- Upgrade networking software regularly. As new versions of

programs come out, it is prudent to upgrade. Security

vulnerabilities will likely have been fixed. The longer you wait

to do this, the greater the risk that security vulnerabilities of

the products will be become known and be exploited by some network

assailant. Keep up to date!

- Find out who to contact if you suspect trouble. Does your

Internet Service Provider have a security contact or Help Desk?

Investigate this before trouble happens so you won't lose time

trying to figure it out should trouble occur. Keep the contact

information both online and offline for easy retrieval.

There are 3 ways to avoid problems with viruses:

1. Don't be promiscuous

If at all possible, be cautious about what software you install on

your system. If you are unaware of or unsure of the origin of a

program, it is wise not to run it. Obtain software from trusted

sources. Do not execute programs or reboot using old diskettes

unless you have reformatted them, especially if the old diskettes

have been used to bring software home from a trade show and other

potentially security-vulnerable places.

Nearly all risk of getting infected by viruses can be eliminated

if you are extremely cautious about what files are stored on your

computer. See "The Dangers of Downloading" for more details.

2. Scan regularly.

Give your system a regular check-up. There are Excellent

virus checking and security audit tools for most computer

platforms available today. Use them, and if possible, set them to

run automatically and regularly. Also, install updates of these

tools regularly and keep yourself informed of new virus threats.

3. Notice the unusual.

It's not true that a difference you cannot detect is no difference

at all, but it is a good rule of thumb. You should get used to

the way your system works. If there is an unexplainable change

(for instance, files you believe should exist are gone, or strange

new files are appearing and disk space is 'vanishing'), you should

check for the presense of viruses.

You should take some time to be familiar with computer virus

detection tools available for your type of computer. You should use

an up-to-date tool (i.e. not older than three months). It is very

important to test your computer if you have been using shared

software of dubious origin, someone else's used floppy disks to

transfer files, and so on.

6.2 What To Do if You Suspect Trouble

If you suspect that your home computer has a virus, that a malicious

program has been run, or that a system has been broken into, the

wisest course of action is to first disconnect the system from all

networks. If available, virus detection or system auditing software

should be used.

Checking vital system files for corruption, tampering or malicious

replacement is very tedious work to do by hand. Fortunately there are

many virus detection programs available for PCs and Macintosh

computers. There are security auditing programs available for

UNIX-based computers. If software is downloaded from the network, it

is wise to run virus detection or auditing tools regularly.

If it becomes clear that a home system has been attacked, it is time

to clean up. Ideally, a system should be rebuilt from scratch. This

means erasing everything on the hard disk. Next, install the

operating system and then all additional software the system needs.

It is best to install the operating system and additional software

from the original distribution diskettes or CD-roms, rather than from

backup storage. The reason for this is that a system may have been

broken into some time ago, so the backed up system or program files

may already include some altered files or viruses. Restoring a system

from scratch is tedious but worthwhile. Do not forget to re-install

all security related fixes you had installed before the security

incident. Obtain these from a verified, unsuspicious source.

6.3 Email

Remember to be careful with saved Email. Copies of sent or received

Email (or indeed any file at all) placed in storage provided by an

Internet service provider may be vulnerable. The risk is that

someone might break into the account and read the old Email. Keep

your Email files, indeed any sensitive files, on your home machine.

7. Home Alone

A home system can be broken into over the Internet if a home user is

unwary. The files on the home system can be stolen, altered or

destroyed. The system itself, if compromised, could be accessed

again some time in the future. This section describes issues and

makes recommendations relevant to a home user of the Internet.

7.1 Beware of Daemons

A home system which uses PPP to connect directly to the Internet is

increasingly common. These systems are at the greatest risk if they

run certain kinds of programs called "services". If you run a

service, you are in effect making your computer available to others

across the network. Some services include:

- File servers (an NFS server, a PC with 'file sharing' turned on)

- An FTP server

- A Web server

There are, in general, two types of programs which operate on the

Internet: Clients (like web browsers and Email programs) and Servers

(like web servers and mail servers).

Most software which runs on home systems is of the client variety;

but, increasingly, server software is available on traditionally

client platforms (e.g., PCs). Server software which runs in the

background is referred to as a "daemon" (pronounced dee-mon). Many

Internet server software programs that run as daemons have names that

end in `d', like "inetd" (Internet Daemon) and "talkd" (Talk Daemon).

When set to run, these programs wait for clients to request some

particular service from across the network.

There are four very important things to keep in mind as far as the

security implications of running services on a home computer are

concerned.

- First and most important, if a server is not properly configured,

it is very vulnerable to being attacked over a network. It is

vital, if you run services, to be familiar with the proper

configuration. This is often not easy, and may require training

or technical expertise.

- All software has flaws, and flaws exploited deviously can be used

to breach computer security. If you run a server on your home

machine, you have to stay aware. This requires work: You have to

stay in touch with the supplier of the software to get security

updates. It is highly recommended that you keep up with security

issues through on-line security forums. See [RFC2196] for a list

of references.

If security flaws in your server software are discovered, you will

need to either stop using the software or apply "patches" or

"fixes" which eliminate the vulnerability. The supplier of the

software, if it is a decent company or freeware author, will

supply information and updates to correct security flaws. These

"patches" or "fixes" must be installed as soon as possible.

- As a rule of thumb, the older the software, the greater the chance

that it has known vulnerabilities. This is not to say you should

simply trust brand new software either! Often, it takes time to

discover even obvious security flaws in servers.

- Some servers start up without any warning. There are some web

browsers and telnet clients which automatically start FTP servers

if not explicitly configured to not do so. If these servers are

not themselves properly configured, the entire file system of the

home computer can become available to anyone on the Internet.

In general, any software MAY start up a network daemon. The way to

be safe here is to know the products you are using. Read the manual,

and if any questions arise, call the company or mail the author of

free software to find out if you are actually running a service by

using the product.

A home user running a remote login service on his home machine faces

very serious risks. This service allows the home user to log in to

his home machine from other computers on the Internet and can be

quite convenient. But the danger is that someone will secretly

observe the logging in and then be able to masquerade as the user

whenever they choose to do so in the future. See "The Wires Have

Ears" which suggests precautions to take for remote log in.

If possible, activate all "logging" options in your server software

which relate to security. You need to review these logs regularly in

order to gain any benefit from this logging. You should also be

aware that logs often grow very quickly in size, so you need to be

careful they don't fill up your hard disk!

7.2 Going Places

Remote logins allow a user privileged access onto physically remote

systems from the comfort of his own home.

More and more companies are offering their employees the ability to

work from home with access to their computer accounts through dial-up

connections. As the convenience of Internet connectivity has led to

lowered costs and wide-spread availability, companies may allow

remote login to their systems via the Internet. Customers of

companies with Internet access may also be provided with remote login

accounts. These companies include Internet service providers, and

even banks. Users should be very careful when making remote logins.

As discussed in "The Wires have Ears" section, Internet connections

can be eavesdropped on. If you intend to use a remote login service,

check that the connection can be done securely, and make sure that

you use the secure technologies/features.

Connections may be secured using technologies like one-time

passwords, secure shell (SSH) and Secure Sockets Layer (SSL). One-

time passwords make a stolen password useless to steal, while secure

shell encrypts data sent over the connection. Please refer to "Don't

Get Caught in the Web" for a discussion on SSL. Secure services such

as these have to be made available on the systems to which you log in

remotely.

7.3 Secure It!

Administering your own home computer means you get to choose what

software is run on it. Encryption software provides protection for

data. If you keep business records and other sensitive data on your

computer, encryption will help to keep it safe. For example, if you

ran a network service from your home computer and missed setting

restrictions on a private directory, a remote user (authorized or

not) may gain access to files in this private directory. If the

files are encrypted, the user will not be able to read them. But as

with all forms of encryption running on any system, the keys and

passwords should first be kept safe!

8. A Final Note

This document has provided the reader with an introduction and as

much concise detail as possible. Present security issues go out of

date quickly, and although effort has been made to keep discussions

general, examples given may not be relevant in the future as the

Internet and computer industry continue to grow.

Just as home-owners are now taking increased cautions at the expense

of convenience, to secure their homes in the changing world we live

in, computer network users should not ignore security. It may be

inconvenient, but it is always better to be safe than sorry.

Appendix: Glossary of Security Terms

Acceptable Use Policy (AUP)

A set of rules and guidelines that specify in more or less detail

the expectations in regard to appropriate use of systems or

networks.

Account

See (Computer) Account

Anonymous and Guest Log In

Services may be made available without any kind of authentication.

This is commonly done, for instance, with the FTP protocol to

allow anonymous access. Other systems provide a special account

named "guest" to provide access, typically restricting the

privileges of this account.

Auditing Tool

Tools to analyze computer systems or networks in regard to their

security status or in relation to the set of services provided by

them. COPS (Computer Oracle Password and Security analyzer) and

SATAN (Security Administrator's Tool for Analyzing Networks) are

famous examples of such tools.

Authentication

Authentication refers to mechanisms which are used to verify the

identity of a user. The process of authentication typically

requires a name and a password to be supplied by the user as proof

of his identity.

Centrally-Administered Network

A network of systems which is the responsibility of a single group

of administrators who are not distributed but work centrally to

take care of the network.

Certificate

Certificates are data which is used to verify digital signatures.

A certificate is only as trustworthy as the agency which issued

it. A certificate is used to verify a particular signed item,

such as an Email message or a web page. The digital signature,

the item and the certificate are all processed by a mathematical

program. It is possible to say, if the signature is valid, that

"According to the agency which issued the certificate, the signer

was (some name)".

Clean System

A computer which has been freshly installed with its operating

system and software obtainied from trusted software distribution

media. As more software and configuration are added to a

computer, it becomes increasingly difficult to determine if the

computer is 'clean' or has been compromised by viruses, trojan

horse or misconfiguration which reduces the security of the

system.

Client

Depending on the point of view, a client might be a computer

system which an end-user uses to access services hosted on another

computer system called a server. 'Client' may also refer to a

program or a part of a system that is used by an end-user to

access services provided by another program (for example, a web

browser is a client that accesses pages provided by a Web Server).

Compound Documents

A 'document' is a file containing (a set of) data. Files may

consist of multiple parts: a plain document, an encrypted

document, a digitally-signed documents or a compressed document.

Multi-part files are known as compound documents and may require a

variety of programs to be used in order to interpret and

manipulate it. These programs may be used without the user's

knowledge.

(Computer) Account

This term describes the authorization to access a specific

computer system or network. Each end-user has to use an account,

which consists most probably of a combination of user name and

password or another means of proving that the end-user is the

person the account is assigned to.

Configuring Network Services

The part of an administrator's task that is related to specifying

the conditions and details of network services that govern the

service provision. In regard to a Web server, this includes which

Web pages are available to whom and what kind of information is

logged for later review purposes.

Cookies

Cookies register information about a visit to a web site for

future use by the server. A server may receive information of

cookies of other sites as well which create concern in terms of

breach of privacy.

Cracker

This term is used to describe attackers, intruders or other bad

guys that do not play by the rules and try to circumvent security

mechanisms and/or attack individuals and organisations.

Daemons (inetd, talkd, etc.)

These are processes that run on computer systems to provide

services to other computer systems or processes. Typically,

daemons are considered "servers".

Decrypting

The process of reversing the encryption of a file or message to

recover the original data in order to use or read it.

Default Account

Some systems and server software come with preconfigured accounts.

These accounts may be set up with a predefined (user name and)

password to allow anyone access and are often put there to make it

convenient for users to login initially. Default accounts should

be turned off or have their predefined passwords changed, to

reduce the risk of abuse to the system.

Dial-in Service

A way of providing access to computer systems or networks via a

telecommunications network. A computer uses a modem to make a

telephone call to a another modem, which in turn provides 'network

access service'. See also: PPP.

Digital Signature

A digital signature is created by a mathematical computer program.

It is not a hand-written signature nor a computer-produced picture

of one. The signature is like a wax seal that requires a special

stamp to produce it, and is attached to an Email message or file.

The origin of the message or file may then be verified by the

digital signature (using special tools).

Downloaded Software

Software packages retrieved from the Internet (using, for example,

the FTP protocol).

Downloading

The act of retrieving files from a server on the network.

Email Packages

To communicate via electronic mail, an end-user usually makes use

of an Email client that provides the user-interface to create,

send, retrieve and read Email. Various different Email packages

provide the same set of basic functions but have different user-

interfaces and perhaps, special/extra functions. Some Email

packages provide encryption and digital signature capabilities.

Email Security Software

Software which provides security through digital signatures and

encryption (and decryption) to enable the end-user to protect

messages and documents prior to sending them over a possibly

insecure network. PGP is an example of such software.

Encrypting / Encryption

This is a mathematical process of scambling data for privacy

protection.

Encryption Software

The software that actually provides the needed functionality for

end users to encrypt messages and files. PGP is one example.

End-User

An (human) individual that makes use of computer systems and

networks.

Files (programs, data, text and so on)

Files include user data, but also programs, the computer operating

system and the system's configuration data.

File Server

A computer system that provides a way of sharing and working on

files stored on the system among users with access to these files

over a network.

File Transfer

The process of transferring files between two computer systems

over a network, using a protocol such as FTP or HTTP.

Fixes, Patches and installing them

Vendors, in response to the discovery of security vulnerabilities,

provide sets of files that have to be installed on computer

systems. These files 'fix' or 'patch' the computer system or

programs and remove the security vulnerability.

FTP (File Transfer Protocol)

A protocol that allows for the transfer of files between an FTP

client and FTP server.

Group of Users

Security software often allow permissions to be set for groups (of

users) as opposed to individuals.

Help Desk

A support entity that can be called upon to get help with a

computer or communication problem.

Internet

A collection of interconnected networks that use a common set of

protocols called the TCP/IP stack to enable communication between

the connected computer systems.

Key Escrow

Keys are used to encrypt and decrypt files. key escrow is used to

store keys for use by third parties to access the data in

encrypted files.

Keys Used to Encrypt and Decrypt Files

To make use of encryption, an end-user has to provide some secret,

in the form of some data, usually called a key.

Log In, Logging into a System

This is an action performed by an end-user, when he authenticates

himself to a computer system.

Log In Prompt

The characters that are displayed when logging into a system to

ask for user name and password.

Logged In

If an end-user has successfully proven to have legitimate access

to a system, he is considered to be logged in.

Logging

Systems and server software often provide the ability to keep

track of events. Events may be configured to be written out to a

file known as a log. The log file can be read later and allows

for system failures and security breaches to be identified.

Masquerade (see Remote Log In)

Anyone who pretends to be someone they are not in order to obtain

access to a computer account is said to be in 'masquerade'. This

may be accomplished by providing a false user name, or stealing

someone else's password and logging in as him.

Network File System (NFS, file sharing with PCs, etc.)

NFS is an application and protocol suite that provides a way of

sharing files between clients and servers. There are other

protocols which provide file access over networks. These provide

similar functionality, but do not interoperate with each other.

Networking Features of Software

Some software has features which make use of the network to

retrieve or share data. It may not be obvious that software has

networking features.

Network Services

Services which are not provided on the local computer system the

end-user is working on but on a server located in the network.

One-Time Passwords (OTP)

Instead of using the same password over and over again, a

different password is used on each subsequent log in.

Passphrase

A passphrase is a long password. It is often composed of several

words and symbols to make it harder to guess.

Password-Locked Screensaver

A screen saver obscures the normal display of a monitor. A

password-locked screensaver can only be deactivated if the end-

user's password is supplied. This prevents a logged-in system

from being abused and hides the work currently being done from

passers-by.

Patch

See "Fixes, Patches and installing them"

Permissions

Another word for the access controls that are used to control the

access to files and other resources.

PGP (Pretty Good Privacy)

PGP is an application package that provides tools to encrypt and

digitally sign files on computer systems. It is especially useful

to encrypt and/or sign files and messages before sending them via

Email.

Plug-in Modules

Software components that integrate into other software (such as

web browsers) to provide additional features.

Point-of-Contact, Security

In case of security breaches or problems, many organisations

provide a designated point-of-contact which can alert others and

take the appropriate actions.

PPP (Point to Point Protocol)

PPP is the mechanism which most end-users establish a network

connection between their PC and their Internet service provider

with. Once connected, the PC is able to transmit and receive data

to any other system on the network.

Privacy Programs

Another term for encryption software that highlights the use of

this software to protect the confidentiality and therefore privacy

of the end-users that make use of it.

Remote Access Software

This software allows a computer to use a modem to connect to

another system. It also allows a computer to 'listen' for calls

on a modem (this computer provides 'remote access service'.)

Remote access software may provide access to a single computer or

to a network.

Remote Log In

If an end-user uses a network to log in to a system, this act is

known as remote log in.

Security Features

These are features which provide protection or enable end-users

and administrators to assess the security of a system, for

example, by auditing it.

Security Policy

A security policy is written by organisations to address security

issues, in the form of "do's" and "don'ts". These guidelines and

rules are for users with respect to physical security, data

security, information security and content (eg. rules stating that

sites with sexual content should not be visited, and that

copyrights should be honoured when downloading software, etc).

Server

A server is a computer system, or a set of processes on a computer

system providing services to clients across a network.

Shared Account

A common account is one which is shared by a group of users as

opposed to a normal account which is available to only one user.

If the account is misused, it is very difficult or impossible to

know which of users was responsible.

Sharing Permissions

Many computer systems allow users to share files over a network.

These systems invariably provide a mechanism for users to use to

control who has permission to read or overwrite these files.

Site

Depending on the context in which this term is used, it might

apply to computer systems that are grouped together by

geographical location, organizational jurisdiction, or network

addresses. A Site typically refers to a network under a common

administration.

SSH (Secure Shell)

SSH provides a protocol between a client and server, allowing for

encrypted remote connectivity.

SSL (Secure Sockets Layer)

This protocol provides security services to otherwise insecure

protocols which operate over a network. SSL is typically used by

web browsers to encrypt data sent to and downloaded from a server.

Systems Administrator

The individual who maintains the system and has system

administrator privileges. In order to avoid errors and mistakes

done by this individual while not acting as an administrator,

he/she should limit the time he/she acts as an administrator (as

known to the system) to a minimum.

System Administrator Privileges

System administrators have more rights (greater permissions) as

their work involve the maintenance of system files.

System Files

The set of files on a system that do not belong to end-users,

which govern the functionality of the system. System files have

a great impact on the security of the system.

Telnet

A protocol that enables remote log in to other computer systems

over the network.

Terminal

A dumb device that is connected to a computer system in order to

provide (text-based) access to it for users and administrators.

Terms of Service (TOS)

See "Acceptable Use Policy (AUP)".

Threats

The potential that an existing vulnerability can be exploited to

compromise the security of systems or networks. Even if a

vulnerability is not known, it represents a threat by this

definition.

Trojan Horse

A program which carries within itself a means to allow the creator

of the program access to the system using it.

Virus

A program which replicates itself on computer systems by

incorporating itself (secretly and maliciously) into other

programs. A virus can be transferred onto a computer system in a

variety of ways.

Virus-Detection Tool

Software that detects and possibly removes computer viruses,

alerting the user appropriately.

Vulnerability

A vulnerability is the existence of a weakness, design, or

implementation error that can lead to an unexpected, undesirable

event compromising the security of the system, network,

application, or protocol involved.

Web Browser Cache

This is the part of the file system that is used to store web

pages and related files. It can be utilized to reload recently

accessed files from the cache instead of loading it every time

from the network.

Web Browser Capabilities

The set of functionalities on a web browser for use by the end-

user. This includes the set of plug-ins available.

Web Server

A server program that provides access to web pages. Some web

servers provide access to other services, such as databases, and

directories.

Worm

A computer program which replicates itself and is self-

propogating. Worms, as opposed to viruses, are meant to spawn in

network environments.

Acknowledgments

The User Security Handbook was a collaborative effort of the Site

Security Handbook Working Group of the IETF. There were also others

who made significant contributions --- Simson Garfinkle and Eric

Luiijf provided very helpful feedback on this document. The Glossary

contribution by Klaus-Peter Kossakowski is much appreciated.

References

[GLOSSARY] Malkin, G., Ed., "Internet User's Glossary", FYI 18, RFC

1983 August 1996.

[RFC2196] Fraser, B., Ed., "Site Security Handbook", FYI 8, RFC2196

September 1997.

Security Considerations

This document discusses what computer users can do to improve

security on their systems.

Authors' Addresses

Erik Guttman

Sun Microsystems

Bahnstr. 2

74915 Waibstadt

Germany

Phone: +49 7263 911701

EMail: erik.guttman@sun.com

Lorna Leong

COLT Internet

250 City Road

City Forum, London

England

Phone: +44 171 390 3900

EMail: lorna@colt.net

Gary Malkin

Bay Networks

8 Federal Street

Billerca, MA 01821

USA

Phone: +1 508 916 4237

EMail: gmalkin@baynetworks.com

Full Copyright Statement

Copyright (C) The Internet Society (1999). All Rights Reserved.

This document and translations of it may be copied and furnished to

others, and derivative works that comment on or otherwise explain it

or assist in its implementation may be prepared, copied, published

and distributed, in whole or in part, without restriction of any

kind, provided that the above copyright notice and this paragraph are

included on all such copies and derivative works. However, this

document itself may not be modified in any way, such as by removing

the copyright notice or references to the Internet Society or other

Internet organizations, except as needed for the purpose of

developing Internet standards in which case the procedures for

copyrights defined in the Internet Standards process must be

followed, or as required to translate it into languages other than

English.

The limited permissions granted above are perpetual and will not be

revoked by the Internet Society or its successors or assigns.

This document and the information contained herein is provided on an

"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING

TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING

BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION

HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF

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