How to test for network security vulnerability

Security vulnerability in any network can be found and exploited by hackers and others in no time. The only questions are when this will happen and how much damage an individual could do once they’ve gained access to the network.

Recognising this reality, most organisations test their own networks for security weaknesses, whether to meet compliance requirements or simply as a best practice. Those that aren’t doing this now should start—the sooner, the better.

There are a variety of methods that can be used for these tests, each of which has its strengths and weaknesses. For example, some can be performed relatively quickly and easily, while others are more complex and exhaustive. Determining which method is right for a particular organisation or situation can be overwhelming to say the least, particularly for those lacking advanced IT skills. The below overview of the most common testing practices will help make sense of the often-confusing array of options to help organisations ensure the highest level of network security and protection.

Vulnerability scans

Vulnerability scans rely on mostly automated tools to find potential vulnerabilities at either the network or application level. Of the two, network scans are the more basic, looking for known common vulnerabilities in widely used commercial and open source software and reporting any that are found with ratings that identify the level of severity.

The advantages of network vulnerability scans lie in their speed, cost efficiency, and safety, which make them ideal for ensuring that the latest system patches and updates have been deployed and that security configurations are as stringent as possible. When run on a regular basis, these scans can serve as an early warning that software is out of date or patches are missing or misconfigured.

Many organisations only test their networks from the Internet. It’s true that Internet facing-vulnerabilities are the most well-known and well-publicised and may seem like the easiest for an attacker to exploit, but there’s much more to the story. Specifically, by limiting scans only to external threats, organisations remain unaware of exactly what an attacker could accomplish once the network has been breached, for example by tricking a user into installing a backdoor via a phishing email. What internal network vulnerabilities could an attacker exploit to move between systems once they’ve gained a foothold? Without testing internally, there’s no way to know the answer to this question until it’s too late.

Organisations must also test from inside the firewall to discover what an attacker could accomplish once the network has been breached

Internal network scans

Therefore, in addition to network vulnerability scans, organisations must also test from inside the firewall. But it’s important to note that even internal network scans can leave blind spots since, by default, scanners only check services that listen for network communications. Unfortunately, many attacks are made possible by phishing, drive-by-downloads, and other campaigns which target web browsers, PDF viewers and other client software that a network scan will skip over. Using these tactics, attackers can then exploit vulnerabilities in other local operating systems to gain administrator privileges.

There is a way to eliminate these blind spots by configuring scanning tools with authentication credentials that enable them to log in to their targets during internal scans, allowing them to check local software as well. This approach will give the most complete view of the status of an organisation’s patches and configurations.

The other main shortcoming of network vulnerability scanners is that they are only as good as their vulnerability signatures, which are based on existing databases of known vulnerabilities. This means they cannot identify flaws that haven’t yet been reported publicly, including those found in more obscure or custom applications. This can present significant risk, as attackers regularly target and leverage vulnerabilities in custom applications to access the data they contain or breach the underlying network. This is where application vulnerability scans come in.

Application scanners

Application scanners are designed specifically to identify these previously undocumented vulnerabilities found in custom applications. Unlike network scanners, these tools exercise all of an application’s functionality to find common types of flaws, rather than looking for a list of known vulnerabilities. However, because of the amount of data these scanners send to an application, they must be used very carefully. No organisation wants to become another entry on the long list of stories about application scanners dumping garbage data into a database or triggering thousands of emails.

That said, regardless of how advanced application scanners may be, they are still incapable of catching a number of vulnerabilities, especially those that are too subtle for the scanner to pick up on but which would be obvious to a human observer. As is the case with network scans, a clean report by an application scanner is a good start but is no guarantee that there are no problems. Organisations should build on these scans with deeper, more complex and thorough methods, such as penetration testing.

Penetration testing brings skilled, "white hat" hackers into the mix to simulate real-world attacks

Real-world testing

Organisations often make the mistake of concentrating their network security efforts on fixing only those vulnerabilities identified by scans as being critical or high-severity in nature, which is a highly ineffective practice. Why? Because real-world breaches are rarely perpetrated on the basis of a single critical network vulnerability. Instead, attackers recognise the tendency to focus on only “serious” problems and often chain together multiple low- to medium-severity network vulnerabilities or combine them with “local” vulnerabilities that are invisible from the network.

Building on network and application vulnerability scanning, penetration testing brings skilled, “white hat” hackers into the mix to simulate the kind of real-world attacks against an organisation’s network services, applications, or even both simultaneously. Like malicious attackers, these testers attempt to combine vulnerabilities uncovered by scanners while also looking for those that the scanners are incapable of detecting. While this process is more time-consuming and costly than deploying scanning tools alone, it provides a more realistic assessment of just how much effort an actual attacker would need to put forth to breach an organisation’s network and data.

Potential unintended consequences

Each of these network vulnerability testing methods brings its own strengths and weaknesses to the overall security equation, underscoring the reality that no testing— regardless of how important or critical it may be—comes without risk. For example, no matter how careful penetration testers are in their efforts to exploit flaws and vulnerabilities without causing damage, it is always possible that a host would be knocked offline temporarily or data in a database altered.

Organisations need to be aware of these potential unintended consequences. It is important to understand that the skill level of the testers will largely determine the success of testing, so organisations should seek out testers with strong experience and skillsets. One final note is that regardless of how tempting it may be to cut costs by limiting the scope of testing, the potential long-term costs—network disruption, data theft, damage to reputation, etc.—could be far greater than today’s savings. For this reason alone, the higher cost to an organisation of having an established, experienced team perform exhaustive testing can actually turn out to be a tremendous bargain.

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