Why is Internet Security So Hard?


Nov 2, 2013 (4 years and 6 months ago)


Why is Internet Security
So Hard?

Dr. Stephen Kent

Chief Scientist

Information Security

Internet Security

Security for the Internet includes both security for
network operations and security for network users

The former is usually the purview of ISPs, the
latter is a shared responsibility among users, ISPs,
and vendors

For network users, there is a need to secure
information on computers and in transit across the

This presentation focuses on security for Internet

What is Security?

ISO 7498
2 defines five security services

Confidentiality (secrecy)

Authentication (identify verification)


Access control

repudiation (not “taking back” what one “said”)

Users also would likely include

Preventing spam

Preventing denial of service


Information Security Disciplines

Physical security

Procedural security

Personnel security

Compromising emanations security

Operating system security

Communications security

a failure in any of these areas can
undermine the security of a system

Security Terminology


security flaws in systems


means of exploiting vulnerabilities


technical or procedural means of addressing
vulnerabilities or thwarting specific attacks


motivated adversaries capable of mounting attacks
which exploit vulnerabilities

Adversaries (The Bad Guys)


Disgruntled employees

Industrial spies


Special interest groups


Real spies

Criminals (organized or otherwise)

Adversary Characteristics


Network wiretapping

Remote attacks against operating systems or

“Social engineering” (e.g., SPAM)

Physical attacks

Personnel subversion





Aversion to detection


The simple characterization of our problem is the
existence of vulnerabilities in products

We face a two sorts of vulnerability problems:

Known vulnerabilities

Unknown vulnerabilities

For known vulnerabilities we can deploy specific

For unknown vulnerabilities, at best we try to
prevent/detect behavior that might be exploiting
these vulnerabilities

Sources of Vulnerabilities

Design flaws

operating system & application vulnerabilities

protocol design vulnerabilities

Implementation flaws

programming errors

undocumented system & application “features”


unintended and/or residual authorizations

failure to deploy security bug fixes

Security Continuum

There are no perfect, secure systems

Systems are "adequately secure" only relative to a
perceived threat

Absence of obvious insecurities is not a good
indication that a system is adequately secure

Risk analysis, if properly performed, provides a
methodology for identifying what constitutes
adequate security

The Threshold Effect

Once a technical attack against a security
technology has been "debugged" it can be
executed by a wide range of (inexperienced)

A technical attack that can be effected using
inexpensive hardware or software is especially
easy to transfer from sophisticated attackers to

Thus it is dangerous to dismiss an attack as "too
complex or too technical" because the perceived
attackers do not possess the technical capability to
mount the attack

Why are the Bad Guys Winning?

Most vendor software has poor security

Too complex

Badly designed


Most users are sloppy

Don’t install the latest patches

Easily tricked (social engineering)

Poor password choices, password reuse, …

Hackers value their time at 0, but user have other
priorities in life!

Common Defense Strategies


Intrusion Detection Systems

virus technology (in hosts and in mail

spam technology (in hosts and in mail

Periodic penetration testing (enterprise nets)

Centralized patch management (enterprise nets)

DOS mechanisms (ISPs)


Recently renamed Intrusion Prevention Devices
(IPDs), probably to help sell more of them :

The term covers a wide range of technologies,
from simple, stateless packet filtering, to
specific devices

At the low end, these offer minimal protection
against most adversaries

At the high end they are expensive and often
interact badly with new applications

In all cases, management of the firewall rule sets
is complex, time consuming, and thus imperfect

Intrusion Detection Systems (IDSs)

An IDS attempts to:

Detect behavior that exploits known vulnerabilities

Detect behavior that might exploit some class of unknown

Detect behavior that might be a precursor to an attack

IDS may attempt to:

Detect signatures of known attacks

Detect anomalous behavior

Do both

IDS’s tend to work poorly, because of the ambiguities
associated with attempts to deal with unknown attacks or
to define “normal” behavior

False positives (incorrect flagging of traffic as “evil” is
common, and makes these systems hard to use

virus Systems

These attempt to detect viruses (and worms),
typically distributed via e
mail attachments or
other forms of file transfer

Usually they are signature based, which means
they know only about previously
detected viruses

A network manager or user has to acquire
signature list updates periodically, or become
vulnerable to newer viruses

These can be effective if properly managed, but
people are sloppy, and virus writers are prolific

spam Technology

The problem with spam is that it is impossible to
distinguish from legitimate mail, in the worst case

Some anti
spam technology works on signatures,
like anti
virus technology, but it is not very
effective because spam generation software does
not focus on software vulnerabilities, like viruses

Some anti
spam technology is based on Baysean
filters (probabilistic measures), but it too is subject
to false positive/false negative tuning problems

Spam is of value to its senders primarily because
users are greedy or naïve; solving this is NOT a
technical problem

Penetration Testing

This is an approach used by many enterprises, but
rarely by individual users

At the low end it is automated, mostly a patch
check on end systems and a firewall filer rules

At the high end one pays “experts” to try to break
into your system(s)

The low end is useful as a form of external
checking re good housekeeping

The high end is very expensive

Centralized Patch Management

The notion here is to enable an IT organization to
check the status of end systems and to patch them
before the systems are successfully attacked

Vendors like Cisco and Microsoft offer this as a
service, part of “admission control” to a LAN

This is another form of “good housekeeping”
checking, on a more frequent basis

It is analogous to low end penetration testing, a
form of centrally managed anti
virus updating

BUT, an already
compromised system can avoid
detection if the attacker is clever

DoS Technology

Denial of service attacks seek to make resources
unavailable, typically through overloading network access
lines with lots of traffic

The problem is that it is hard to tell good traffic from bad
traffic out in the Internet (vs. at an end system)

Some systems try to look at traffic flows and discard
packets if the flow to a given destination is “too high”
BUT, good traffic is often discarded as well as bad!

We know that some DoS hackers have thousands of
“zombie” systems available to them, dispersed over the
Internet, to launch attacks, which makes it almost
impossible to counter such attacks without causing
problems for legitimate users as well

Abstraction and Attacks

One strategy for an adversary is to attack below
the layer of abstraction at which security measures
are defined, or via ill
defined interfaces

Complex applications and operating systems like
Windows have many ill
defined interfaces

Security measures implemented in applications (or
middleware) embody high levels of abstraction

The trend is to create more opportunities for an
attacker as we use more complex, high level
application development environments, e.g., web

Security in Products:

Functionality vs. Assurance

Security functions
: usually visible, security
relevant features that provide the means by which
security is invoked and managed

Security assurance
: often invisible means by
which one develops confidence in the correct
operation of security features

Many products now advertise lots of security
functions (because today, security sells), but the
products offer little or no assurance!

Security Assurance

Product security assurance techniques

penetration testing

detailed code review

use of formal specifications

security evaluation criteria

Unfortunately, these techniques are either very
expensive or very haphazard

As a result, we have few products for which we
have a good idea of their security quality

Security & Privacy: A Quick Look



Uniform identification

Extensive auditing

Correlation of audit data

Centralized management

Mediated access to all



Use of diverse identifiers

Limited data collection

No sharing of records

Distributed autonomy

Mediated access to
records that affect

Security and privacy need not be in conflict,
but it takes a lot of effort to balance the two


Internet security is hard because:

Its hard to counter unknown vulnerabilities in products

Even security products themselves often have unknown

The utility of an IDS is limited by feature rich

Most CIOs can’t even track all the systems in their nets

There is no methodology for designing a secure system
from secure components (and we have few secure
components anyway)

Abstraction favors the adversary

Some problems (e.g., spam) are not technical in nature

People are sloppy, greedy, and sometimes naïve