Network Monitoring As A Security Tool

[Excerpted from "Network Monitoring as a Security Tool," a new report published this week on Dark Reading's Security Monitoring Tech Center.]

For most organizations, network monitoring tools are a well-established part of IT operations. They serve the critical role of letting the IT shop know when service quality is impacted -- for example, when network connections are down (or underperforming) or when critical resources such as servers or applications are down. They also help in numerous other ways to keep technology services running smoothly. Seldom, though, are they used in a focused manner by the security team.

This is unfortunate because, in many ways, network monitoring tools can provide direct benefits for the security organization. Not only are many of the events that these tools monitor for symptomatic of security events such as malware or attacker activity, but they're also a useful way to help beef up security in situations where budget is hard to come by. Using network monitoring tools creatively can help add security value, and, because these tools often are already in place, they can provide that value at a comparatively low cost.

Probably the most direct area where a network monitoring tool can add security value is in the arena of denial of service (DoS) conditions. There are a number of different types and varieties of DoS and distributed DoS HTTP-overload attacks, but all DoS conditions, including HTTP-overload attacks, TCP-based DoS (such as SYN floods) or even purposeful user account lockout.

However, all DoS conditions -- whether caused deliberately by an attacker or accidentally -- will share one key characteristic: unavailability of resources. One of the primary use cases for network monitoring tools is monitoring for that condition.

Network asset management tools can also play an important role in security. From a security standpoint, maintaining a reliable asset inventory is of paramount importance. However, it's also a pain point for most organizations.

A reliable inventory is important first of all because that inventory can play a key role in everything from disaster recovery (allowing resources to understand the role and function of systems), to incident management and investigations (to understand what data may have been compromised in an attack), to regulatory compliance (understanding where regulated data is stored and transmitted throughout the environment).

Despite such importance, organizations often find it difficult to maintain a reliable inventory. Changes occur so rapidly in most environments that manually created asset lists can be out of date before they're even finalized, let alone after a few weeks or months have gone by.

Network monitoring products can help in this area because many of these products come with features that assist in data collection, host discovery and inventory. For example, many have the ability to perform SNMP-based discovery or system-specific discovery.

Investigations support is another area where network monitoring tools can be useful. In much the same way that network monitoring tools will provide early warning of DoS attacks, these tools also can assist with incident investigation.

Many of the attack techniques that intruders employ to gain access to systems can result in services or hosts becoming temporarily unavailable. For example, many buffer overflow conditions, when exploited, will cause services to crash, become unresponsive or, in extreme cases, trigger a system halt and subsequent restart. These events happen as a byproduct of conducting the exploit -- for example, when system memory is overwritten with exploit code.

Because network monitoring tools watch for a lack of responsiveness in key services and hosts, events like these are likely to trigger alert conditions. And because the alert is raised by systems other than the now-compromised target of the exploit, they're more tamper- resistant than the application and system logs on the host itself (since many attackers will attempt to cover their tracks by deleting or manipulating system logs).

Network monitoring tools can also help you locate anomalous conditions within the network that could be reflective of attacker activity. Note that there's a whole category of tools made specifically to monitor, for example, traffic spikes via NetFlow or sFlow (network behavioral anomaly detection).

This is not to say it isn't valuable to have an NBAD system, which will be tailored specifically to security use cases like DDoS and data exfiltration. However, in the absence of a security-focused tool, you may be able to get some NBAD value out of your network monitoring tool.

Network monitoring tools that have the capacity to gather performance data from monitored systems -- through the use of WMI, for example -- can allow you to see unexpected patterns of activity that could result from a security event.

For example, unexpectedly high resource allocation (high CPU load, significant network activity,and so on) on a particular host could be reflective of an attack in progress. When paired with information from system logs, IDS or other security tools, this information can help to prioritize which events bear further scrutiny.

To get a detailed description of today's network monitoring tools -- and additional tips for using them to find potential security threats -- download the free report on security and network monitoring.

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