[ISN] Four steps for protecting your internal networks

InfoSec News isn at c4i.org
Mon Sep 13 03:44:28 EDT 2004


Opinion by Mudge
Intrusic Inc.
SEPTEMBER 09, 2004 

In the sciences, there are general principles that can apply to all 
environments. The principles of physics (i.e. the general laws) are 
ubiquitous across disciplines. Why should the information security 
field be any different? It turns out that it isn't. 

In my experience, the following general principles have proved 
beneficial. Companies can apply them with existing internal resources. 

1. Map security around business functions 

In few areas is the relationship of security to business functions 
more obvious than in comparing electrical utilities with industrial 
refineries. Both business models use a segmentation structure around 
Supervisory Control and Data Acquisition and/or distributed control 
systems. While both electrical utilities and refineries have these 
environments, the refineries, in general, have a much more secure 
implementation of this model. Was this due to particular security 
requirements? No. Upon querying technical experts from both 
industries, the rationale became clear: One field had to be much more 
competitive in the business realm than the other. Industrial 
refineries had to compete in the business market, while utilities were 
subsidized and regulated by the government. 

If one company operated at even a fraction of a percentage more 
efficiently and cost-effectively than a competitor did, that business 
had an edge in the public markets. Tremendous amounts of effort were 
spent designing and making networks and systems perform core technical 
requirements in a way that was as efficient and organized as possible. 
These efforts resulted in networks with a relatively high security 
baseline. More important, they provided a solid foundation for future 
security components that might be desired in the future. 

Without the economic driver of competition for the electrical 
utilities, the optimization and maximization of underlying business 
architectures didn't receive the same attention. As various utilities 
markets are deregulated, many players find themselves in the position 
of having to make a profit. However, the underlying infrastructure 
lacks a foundation solid enough to confidently run critical business 
tasks, let alone withstand hostile attacks. 

2. Define information and data labeling and handling guidelines 

Although an arduous initial task, implementing data classification, 
labeling and handling guidelines will pay huge dividends in the long 
run. Many companies will invest substantial capital toward 
vulnerability assessments, network intrusion-detection systems and 
security best-practice guidelines. Unfortunately, few of these 
companies ever embrace information labeling and classification 

If an engineer comes across a business memo he doesn't understand, 
what are the odds that this information will be handled in a secure 
fashion commensurate with the memo's value? Conversely, if a secretary 
receives an e-mail that carries with it an attachment of source code, 
will the secretary automatically know whether it's permissible to 
forward this e-mail to a recipient outside of the corporate network? 
No matter how perfect the technical security might be within an 
organization, not understanding what's valuable or sensitive and how 
to appropriately handle it will negate those technical defenses. 

While I was working with the U.S. government on the problem of 
vulnerabilities in critical infrastructure, data labeling and handling 
guidelines surfaced as one of the most glaring problems. More than 80% 
of the time, there was no need to break into an organization that was 
a key player in one of the critical-infrastructure segments to 
demonstrate key vulnerabilities. Simply engaging in intelligence 
gathering would invariably yield the information to circumvent their 
corporate security or gain direct access to back-end networks 
responsible for the command and control of utility, financial, 
transportation and communications networks. 

3. Learn how your network actually works 

Many companies lack internal network diagrams altogether, let alone 
up-to-date ones. While this might not be surprising, the following 
point very well might be: Of all the "up-to-date" internal network 
diagrams I have seen, only a small fraction of them are accurate in 
their representation of what really transpires on the underlying 

The divergence of actual network routing/flow from many paper mappings 
put together by internal network operations groups is easy to 
understand. The introduction or removal of network devices (primarily 
routers, switches and hubs in this case) without documentation or the 
knowledge of IT is an obvious culprit. This can be accidental or 
intentional. While this does happen, it's usually not the greatest 
contributor to inaccurate network maps. 

The larger contributor comes in two parts. First is the use of dynamic 
protocols in an inherently static environment. The second is the 
willingness to forget the fact that most network infrastructure 
devices intentionally "fail open." 

Few internal networks are set up with multiple entry and exit points. 
There is usually a single router per network or subnet that connects 
each leg to form the corporate network. Yet it's tremendously common 
to find internal routers running dynamic routing and discovery 
protocols. Because of this, normal maintenance of infrastructure 
components or reconfiguration of individual elements can result in 
cascading modifications to routes and paths. There are many suboptimal 
ways of switching and/or routing traffic that will continue to provide 
base functionality (albeit at a cost of performance and complexity). 
Why is it that so many organizations have infrastructure devices 
configured to use dynamic routing and/or discovery protocols? The 
answer is simple: Vendors ship them by default. 

Manufacturers of infrastructure devices have to make a choice as to 
how their equipment will act under unusual or unknown circumstances. 
Should the expensive switch stop working entirely, or should it revert 
to broadcast mode where it acts more akin to a repeater/hub? The 
choice is obvious. Put yourself in their situation and guess which 
option might be more or less disruptive to the customer's environment. 
Unfortunately, the customer is usually unaware of the fact that a 
switch has failed open. 

The general rule of thumb for both business optimization and security 
is, "Keep it simple." By configuring infrastructure equipment to be 
static if it's deployed in a static environment and including periodic 
promiscuous sampling of network traffic at various locations, you'll 
maintain an accurate understanding of your network. At the very least, 
you'll be more aware of when things change. 

4. Understand the components in your environment and how they relate 
   to business 

By following the above recommendations, this final project is much
easier. This step allows an organization to engage in detecting and
defending against external entities that have gained access to the
network, or from internal personnel with ulterior motives.

Standard intrusion-detection systems won't identify these threats
because they're already inside. They don't attack a system because
access is implicitly granted. The activities engaged in won't be
detected, nor will they be thwarted by patching vulnerabilities
discovered through network vulnerability assessments. One must engage
in more classical counterintelligence practices to effectively combat
this threat.

Let's say that these steps are in place: Business functions have been
made as efficient as possible and are realistically mapped through
their corresponding optimized network flows; corporatewide information
and data classification and guidelines are in place, and network maps
are known beyond any doubt to accurately represent how packets and
information actually flow. Now it's possible to identify
information-gathering and reconnaissance activities, data removal and
passive control of systems by covert adversaries.

Adversaries have more to gain by maintaining access to internal
networks for as long as possible without being discovered. However, to
move data outside of this constrained environment, they must engage in
activities that bend, if not flat-out violate, the general economics
and information-theory principles of soundly designed and run
businesses. Soundly run businesses by necessity require soundly
understood internal networks and data items.

Peiter Mudge Zatko is founding scientist of Waltham, Mass.-based
Intrusic Inc. and a division scientist at Cambridge, Mass.-based BBN

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