Ethical Hacking
The term “hacker” has a dual usage in the computer
industry today. Originally, the term was
defined as:
HACKER noun 1.Aperson who enjoys learning the
details of computer systems and how to stretch
their capabilities—as opposed to most users of
computers, who prefer to learn only the minimum
amount necessary. 2. One who programs enthusiastically
or who enjoys programming rather than
just theorizing about programming.1
This complimentary description was often extended
to the verb form “hacking,” which was used to describe
the rapid crafting of a new program or the
making of changes to existing, usually complicated
software.
As computers became increasingly available at universities,
user communities began to extend beyond
researchers in engineering or computer science to
other individuals who viewed the computer as a curiously
flexible tool. Whether they programmed the
computers to play games, draw pictures, or to help
them with the more mundane aspects of their daily
work, once computers were available for use, there
was never a lack of individuals wanting to use them.
Because of this increasing popularity of computers
and their continued high cost, access to them was
usually restricted. When refused access to the computers,
some users would challenge the access controls
that had been put in place. They would steal
passwords or account numbers by looking over someone’s
shoulder, explore the system for bugs that
might get them past the rules, or even take control
of the whole system. They would do these things in
order to be able to run the programs of their choice,
or just to change the limitations under which their
programs were running.
Initially these computer intrusions were fairly benign,
with the most damage being the theft of computer
time. Other times, these recreations would take the
form of practical jokes. However, these intrusions did
not stay benign for long. Occasionally the less talented,
or less careful, intruders would accidentally bringdown
a system or damage its files, and the system administrators
would have to restart it or make repairs. Other
times, when these intruders were again denied access
once their activities were discovered, they would
react with purposefully destructive actions.Whenthe
number of these destructive computer intrusions became
noticeable, due to the visibility of the system
or the extent of the damage inflicted, it became
“news” and the news media picked up on the story.
Instead of using the more accurate term of “computer
criminal,” the media began using the term
“hacker” to describe individuals who break into computers
for fun, revenge, or profit. Since calling someone
a “hacker” was originally meant as a compliment,
computer security professionals prefer to use the
term “cracker” or “intruder” for those hackers who
turn to the dark side of hacking. For clarity, we will
use the explicit terms “ethical hacker” and “criminal
hacker” for the rest of this paper.
What is ethical hacking?
With the growth of the Internet, computer security
has become a major concern for businesses and governments.
They want to be able to take advantage
of the Internet for electronic commerce, advertising,
information distribution and access, and other
pursuits, but they are worried about the possibility
of being “hacked.” At the same time, the potential
customers of these services are worried about maintaining
control of personal information that varies
from credit card numbers to social security numbers
and home addresses.2
In their search for a way to approach the problem,
organizations came to realize that one of the best
ways to evaluate the intruder threat to their interests
would be to have independent computer security
professionals attempt to break into their computer
systems. This scheme is similar to having
independent auditors come into an organization to
verify its bookkeeping records. In the case of computer
security, these “tiger teams” or “ethical hackers”
3 would employ the same tools and techniques
as the intruders, but they would neither damage the
target systems nor steal information. Instead, they
would evaluate the target systems’ security and report
back to the owners with the vulnerabilities they
found and instructions for how to remedy them.
This method of evaluating the security of a system
has been in use from the early days of computers.
In one early ethical hack, the United States Air Force
conducted a “security evaluation” of the Multics operating
systems for “potential use as a two-level
(secret/top secret) system.” 4 Their evaluation found
that while Multics was “significantly better than other
conventional systems,” it also had “ . . . vulnerabilities
in hardware security, software security, and procedural
security” that could be uncovered with “a
relatively low level of effort.” The authors performed
their tests under a guideline of realism, so that their
results would accurately represent the kinds of access
that an intruder could potentially achieve. They
performed tests that were simple information-gathering
exercises, as well as other tests that were outright
attacks upon the system that might damage its
integrity. Clearly, their audience wanted to know
both results. There are several other now unclassified
reports that describe ethical hacking activities
within the U.S. military.5–7
With the growth of computer networking, and of the
Internet in particular, computer and network vulnerability
studies began to appear outside of the military
establishment. Most notable of these was the
work by Farmer and Venema,8 which was originally
posted to Usenet9 in December of 1993. They discussed
publicly, perhaps for the first time,10 this idea
of using the techniques of the hacker to assess the
security of a system. With the goal of raising the overall
level of security on the Internet and intranets, they
proceeded to describe how they were able to gather
enough information about their targets to have been
able to compromise security if they had chosen to
do so. They provided several specific examples of
how this information could be gathered and exploited
to gain control of the target, and how such an attack
could be prevented.
Farmer and Venema elected to share their report
freely on the Internet in order that everyone could
read and learn from it. However, they realized that
the testing at which they had become so adept might
be too complex, time-consuming, or just too boring
for the typical system administrator to perform on
a regular basis. For this reason, they gathered up all
the tools that they had used during their work, packaged
them in a single, easy-to-use application, and
gave it away to anyone who chose to download it.11
Their program, called Security Analysis Tool for Auditing
Networks, or SATAN, was met with a great
amount of media attention around the world. Most
of this early attention was negative, because the tool’s
capabilities were misunderstood. The tool was not
an automated hacker program that would bore into
systems and steal their secrets. Rather, the tool performed
an audit that both identified the vulnerabilities
of a system and provided advice on how to eliminate
them. Just as banks have regular audits of their
accounts and procedures, computer systems also
need regular checking. The SATAN tool provided that
auditing capability, but it went one step further: it
also advised the user on how to correct the problems
it discovered. The tool did not tell the user how
the vulnerability might be exploited, because there
would be no useful point in doing so.
Who are ethical hackers?
These early efforts provide good examples of ethical
hackers. Successful ethical hackers possess a variety
of skills. First and foremost, they must be completely
trustworthy. While testing the security of a
client’s systems, the ethical hacker may discover information
about the client that should remain secret.
In many cases, this information, if publicized,
could lead to real intruders breaking into the systems,
possibly leading to financial losses. During an
evaluation, the ethical hacker often holds the “keys
to the company,” and therefore must be trusted to
exercise tight control over any information about a
target that could be misused. The sensitivity of the
information gathered during an evaluation requires
that strong measures be taken to ensure the security
of the systems being employed by the ethical hackers
themselves: limited-access labs with physical security
protection and full ceiling-to-floor walls, multiple
secure Internet connections, a safe to hold paper
documentation from clients, strong cryptography to
protect electronic results, and isolated networks for
testing.
Ethical hackers typically have very strong programming
and computer networking skills and have been
in the computer and networking business for several
years. They are also adept at installing and maintaining
systems that use the more popular operating
systems (e.g., UNIX** or Windows NT**) used on target
systems. These base skills are augmented with
detailed knowledge of the hardware and software
provided by the more popular computer and networking
hardware vendors. It should be noted that
an additional specialization in security is not always
necessary, as strong skills in the other areas imply
a very good understanding of how the security on
various systems is maintained. These systems management
skills are necessary for the actual vulnerability
testing, but are equally important when preparing
the report for the client after the test.
Finally, good candidates for ethical hacking have
more drive and patience than most people. Unlike
the way someone breaks into a computer in the movies,
the work that ethical hackers do demands a lot
of time and persistence. This is a critical trait, since
criminal hackers are known to be extremely patient
and willing to monitor systems for days or weeks
while waiting for an opportunity. A typical evaluation
may require several days of tedious work that
is difficult to automate. Some portions of the evaluations
must be done outside of normal working
hours to avoid interfering with production at “live”
targets or to simulate the timing of a real attack.
When they encounter a system with which they are
unfamiliar, ethical hackers will spend the time to
learn about the system and try to find its weaknesses.
Finally, keeping up with the ever-changing world of
computer and network security requires continuous
education and review.
One might observe that the skills we have described
could just as easily belong to a criminal hacker as
to an ethical hacker. Just as in sports or warfare,
knowledge of the skills and techniques of your opponent
is vital to your success. In the computer security
realm, the ethical hacker’s task is the harder
one. With traditional crime anyone can become a
shoplifter, graffiti artist, or a mugger. Their potential
targets are usually easy to identify and tend to
be localized. The local law enforcement agents must
know how the criminals ply their trade and how to
stop them. On the Internet anyone can download
criminal hacker tools and use them to attempt to
break into computers anywhere in the world. Ethical
hackers have to know the techniques of the criminal
hackers, how their activities might be detected,
and how to stop them.
Given these qualifications, how does one go about
finding such individuals? The best ethical hacker candidates
will have successfully published research papers
or released popular open-source security software.
12 The computer security community is strongly
self-policing, given the importance of its work. Most
ethical hackers, and many of the better computer and
network security experts, did not set out to focus on
these issues. Most of them were computer users from
various disciplines, such as astronomy and physics,
mathematics, computer science, philosophy, or liberal
arts, who took it personally when someone disrupted
their work with a hack.
One rule that IBM’s ethical hacking effort had from
the very beginning was that we would not hire exhackers.
While some will argue that only a “real
hacker” would have the skill to actually do the work,
we feel that the requirement for absolute trust eliminated
such candidates. We likened the decision to
that of hiring a fire marshal for a school district: while
a gifted ex-arsonist might indeed know everything
about setting and putting out fires, would the parents
of the students really feel comfortable with such
a choice? This decision was further justified when
the service was initially offered: the customers themselves
asked that such a restriction be observed. Since
IBM’s ethical hacking group was formed, there have
been numerous ex-hackers who have become security
consultants and spokespersons for the news media.
While they may very well have turned away from
the “dark side,” there will always be a doubt.
What do ethical hackers do?
An ethical hacker’s evaluation of a system’s security
seeks answers to three basic questions:
c What can an intruder see on the target systems?
c What can an intruder do with that information?
c Does anyone at the target notice the intruder’s attempts
or successes?
While the first and second of these are clearly important,
the third is even more important: If the owners
or operators of the target systems do not notice
when someone is trying to break in, the intruders
can, and will, spend weeks or months trying and will
usually eventually succeed.
When the client requests an evaluation, there is quite
a bit of discussion and paperwork that must be done
up front. The discussion begins with the client’s answers
to questions similar to those posed by Garfinkel
and Spafford:13
1. What are you trying to protect?
2. What are you trying to protect against?
3. How much time, effort, and money are you willing
to expend to obtain adequate protection?
A surprising number of clients have difficulty precisely
answering the first question: a medical center
might say “our patient information,” an engineering
firm might answer “our new product designs,”
and a Web retailer might answer “our customer database.”
All of these answers fall short, since they only describe
targets in a general way. The client usually has
to be guided to succinctly describe all of the critical
information assets for which loss could adversely affect
the organization or its clients. These assets
should also include secondary information sources,
such as employee names and addresses (which are privacy
and safety risks), computer and network information
(which could provide assistance to an intruder),
and other organizations with which this organization
collaborates (which provide alternate paths into the target
systems through a possibly less secure partner’s
system).
A complete answer to (2) specifies more than just
the loss of the things listed in answer to (1). There
are also the issues of system availability, wherein a
denial-of-service attack could cost the client actual
revenue and customer loss because systems were unavailable.
The world became quite familiar with denial-
of-service attacks in February of 2000 when attacks
were launched against eBay**, Yahoo!**,
E*TRADE**, CNN**, and other popularWebsites.
During the attacks, customers were unable to reach
these Web sites, resulting in loss of revenue and
“mind share.” The answers to (1) should contain
more than just a list of information assets on the organization’s
computer. The level of damage to an
organization’s good image resulting from a successful
criminal hack can range from merely embarrassing
to a serious threat to revenue. As an example of
a hack affecting an organization’s image, on January
17, 2000, a U.S. Library of Congress Web site
was attacked. The original initial screen is shown in
Figure 1, whereas the hacked screen is shown in Figure
2. As is often done, the criminal hacker left his
or her nickname, or handle, near the top of the page
in order to guarantee credit for the break-in.
Some clients are under the mistaken impression that
their Web site would not be a target. They cite numerous
reasons, such as “it has nothing interesting
on it” or “hackers have never heard of my company.”
What these clients do not realize is that every
Web site is a target. The goal of many criminal hackers
is simple: Do something spectacular and then
make sure that all of your pals know that you did it.
Another rebuttal is that many hackers simply do not
care who your company or organization is; they hack
your Web site because they can. For example, Web
administrators at UNICEF (United Nations Children’s
Fund) might very well have thought that no hacker
would attack them. However, in January of 1998,
their page was defaced as shown in Figures 3 and
4. Many other examples of hacked Web pages can
be found at archival sites around the Web.14
Answers to the third question are complicated by the
fact that computer and network security costs come
in three forms. First there are the real monetary costs
incurred when obtaining security consulting, hiring.
The ethical hack itself
Once the contractual agreement is in place, the testing
may begin as defined in the agreement. It should
be noted that the testing itself poses some risk to
the client, since a criminal hacker monitoring the
transmissions of the ethical hackers could learn the
same information. If the ethical hackers identify a
weakness in the client’s security, the criminal hacker
could potentially attempt to exploit that vulnerability.
This is especially vexing since the activities of the
ethical hackers might mask those of the criminal
hackers. The best approach to this dilemma is to
maintain several addresses around the Internet from
which the ethical hacker’s transmissions will emanate,
and to switch origin addresses often. Complete
logs of the tests performed by the ethical hackers
are always maintained, both for the final report and
in the event that something unusual occurs. In extreme
cases, additional intrusion monitoring software
can be deployed at the target to ensure that all the
tests are coming from the ethical hacker’s machines.
However, this is difficult to do without tipping off
the client’s staff and may require the cooperation of
the client’s Internet service provider.
The line between criminal hacking and computer virus
writing is becoming increasingly blurred. When
requested by the client, the ethical hacker can perform
testing to determine the client’s vulnerability
to e-mail or Web-based virus vectors. However, it
is far better for the client to deploy strong antivirus
software, keep it up to date, and have a clear and
simple policy in place for the reporting of incidents.
IBM’s Immune System for Cyberspace16,17 is another
approach that provides the additional capability of
recognizing new viruses and reporting them to a central
lab that automatically analyzes the virus and provides
an immediate vaccine.
As dramatized in Figure 5, there are several kinds
of testing. Any combination of the following may be
called for:
c Remote network. This test simulates the intruder
launching an attack across the Internet. The primary
defenses that must be defeated here are border
firewalls, filtering routers, and Web servers.
c Remote dial-up network. This test simulates the intruder
launching an attack against the client’s modem
pools. The primary defenses that must be defeated
here are user authentication schemes. These
kinds of tests should be coordinated with the local
telephone company.
Local network. This test simulates an employee or
other authorized person who has a legal connection
to the organization’s network. The primary
defenses that must be defeated here are intranet
firewalls, internalWebservers, server security measures,
and e-mail systems.
c Stolen laptop computer. In this test, the laptop computer
of a key employee, such as an upper-level
manager or strategist, is taken by the client without
warning and given to the ethical hackers. They
examine the computer for passwords stored in dial-
up software, corporate information assets, personnel
information, and the like. Since many busy
users will store their passwords on their machine,
it is common for the ethical hackers to be able to
use this laptop computer to dial into the corporate
intranet with the owner’s full privileges.
c Social engineering. This test evaluates the target organization’s
staff as to whether it would leak information
to someone. A typical example of this
would be an intruder calling the organization’s
computer help line and asking for the external telephone
numbers of the modem pool. Defending
against this kind of attack is the hardest, because
people and personalities are involved. Most people
are basically helpful, so it seems harmless to
tell someone who appears to be lost where the
computer room is located, or to let someone into
the building who “forgot” his or her badge. The
only defense against this is to raise security awareness.
c Physical entry. This test acts out a physical penetration
of the organization’s building. Special arrangements
must be made for this, since security
guards or police could become involved if the ethical
hackers fail to avoid detection. Once inside
the building, it is important that the tester not be
detected. One technique is for the tester to carry
a document with the target company’s logo on it.
Such a document could be found by digging
through trash cans before the ethical hack or by
casually picking up a document from a trash can
or desk once the tester is inside. The primary defenses
here are a strong security policy, security
guards, access controls and monitoring, and security
awareness.
Each of these kinds of testing can be performed from
three perspectives: as a total outsider, a “semi-outsider,”
or a valid user.
A total outsider has very limited knowledge about
the target systems. The only information used is available
through public sources on the Internet. This test
represents the most commonly perceived threat. A
well-defended system should not allow this kind of
intruder to do anything.
A semi-outsider has limited access to one or more
of the organization’s computers or networks. This
tests scenarios such as a bank allowing its depositors
to use special software and a modem to access
information about their accounts. A well-defended
system should only allow this kind of intruder to access
his or her own account information.
A valid user has valid access to at least some of the
organization’s computers and networks. This tests
whether or not insiders with some access can extend
that access beyond what has been prescribed.Awelldefended
system should allow an insider to access
only the areas and resources that the system administrator
has assigned to the insider.
The actual evaluation of the client’s systems proceeds
through several phases, as described previously by
Boulanger.18
The final report
The final report is a collection of all of the ethical
hacker’s discoveries made during the evaluation.
Vulnerabilities that were found to exist are explained
and avoidance procedures specified. If the ethical
hacker’s activities were noticed at all, the response
of the client’s staff is described and suggestions for
improvements are made. If social engineering testing
exposed problems, advice is offered on how to
raise awareness. This is the main point of the whole
exercise: it does clients no good just to tell them that
they have problems. The report must include specific
advice on how to close the vulnerabilities and
keep them closed. The actual techniques employed
by the testers are never revealed. This is because the
person delivering the report can never be sure just
who will have access to that report once it is in the
client’s hands. For example, an employee might want
to try out some of the techniques for himself or herself.
He or she might choose to test the company’s
systems, possibly annoying system administrators or
even inadvertently hiding a real attack. The employee
might also choose to test the systems of another organization,
which is a felony in the United States
when done without permission.
The actual delivery of the report is also a sensitive
issue. If vulnerabilities were found, the report could
be extremely dangerous if it fell into the wrong hands.
A competitor might use it for corporate espionage,
a hacker might use it to break into the client’s computers,
or a prankster might just post the report’s
contents on the Web as a joke. The final report is
typically delivered directly to an officer of the client
organization in hard-copy form. The ethical hackers
would have an ongoing responsibility to ensure
the safety of any information they retain, so in most
cases all information related to the work is destroyed
at the end of the contract.
Once the ethical hack is done and the report delivered,
the client might ask “So, if I fix these things
I’ll have perfect security, right?” Unfortunately, this
is not the case. People operate the client’s computers
and networks, and people make mistakes. The
longer it has been since the testing was performed,
the less can be reliably said about the state of a client’s
security. A portion of the final report includes
recommendations for steps the client should continue
to follow in order to reduce the impact of these
mistakes in the future.
Conclusions
The idea of testing the security of a system by trying
to break into it is not new. Whether an automobile
company is crash-testing cars, or an individual is testing
his or her skill at martial arts by sparring with
a partner, evaluation by testing under attack from
a real adversary is widely accepted as prudent. It is,
however, not sufficient by itself. As Roger Schell observed
nearly 30 years ago:
From a practical standpoint the security problem
will remain as long as manufacturers remain committed
to current system architectures, produced
without a firm requirement for security. As long
as there is support for ad hoc fixes and security packages
for these inadequate designs and as long as the
illusory results of penetration teams are accepted as
demonstrations of a computer system security, proper
security will not be a reality.
Regular auditing, vigilant intrusion detection, good
system administration practice, and computer security
awareness are all essential parts of an organization’s
security efforts. A single failure in any of
these areas could very well expose an organization
to cyber-vandalism, embarrassment, loss of revenue
or mind share, or worse. Any new technology has its
benefits and its risks. While ethical hackers can help
clients better understand their security needs, it is
up to the clients to keep their guards in place.
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