The computers on your network are protected from malware right? If you are operating an environment based largely on Windows based PCs you likely have some kind of anti-virus installed and centrally managed. If you have purchased a more complete desktop protection suite, you probably even have a Host Based IDS/IPS protecting your machine from incoming malicious TCP scans, or possible outbound connections to known malicious sites (like google.com occasionally). Operating system firewall activated? Yep! AV signatures current? Check! Global Threat Intelligence updated? Uh, yeah....sure. Then you should be covered against threats targeting your organization, right? Most likely not, and at times these tools actually mask intrusions as they provide a false sense of security and protection.

The Trouble with Reactionary Behavior
The problem with these tools, all of them, is that they are purely reactionary in nature. Reactionary protection tools on every level, is something that basically states that an event has already occurred on your host computer, and those protection mechanisms will now activate. That means when you get an antivirus alert on your computer, the malware ALREADY present on the system. Yes, it may have stopped it, deleted it or possibly quarantined it (all of which are good). It has only done so because the AV software either has an existing signature in its database or the malware has attempted to operate in a suspicious manner, flagging the heuristics detection of the AV. What about when brand new malware, 0-day exploits, or sophisticated targeted malware executes on your host?

Do you imagine your AV will detect and mitigate it? I would suggest that your AV will be none the wiser to the presence of this yet to be detected threat, and only once it has been submitted to an AV vendor for analysis will you be provided with an updated signature. Well certainly if my AV missed it, one of the other layers of protection should stop it, right? It is possible, if the malware uses outbound connections that aren't considered "normal" by your OS's firewall or HIDS/HIPS software, then the malware could potentially be detected. If the malware uses standard outbound connections, port 80 or more than likely port 443, this appears as "normal" to the other layers of your systems host based defenses in place.

These tools all require some kind of known characteristics of a particular threat in order to detect its presence and mitigate it. These characteristics are obtained through analysis of reported and discovered threats of a similar nature, of which are used to develop signatures or heuristic models to detect the presence of malware on a host. If that threat has not yet been submitted for analysis and the callback domains not reported as malicious, it may be a while for it to be "discovered" and signatures made available. Until that time, your computer, its files, all of your activities as well as other computers on your network are at the mercy of an attacker unabated.

Being Proactive Is Essentially Free
This is the part that is really frustrating for me as an analyst, and also as an advocate for root cause solutions. Reactionary defenses cost an unreal amount of money for consumers, businesses, governments (both state and local), federal and military. You would think with all of this time and money spent on the various products billed as "protecting" you from cyber threats & intrusions, your environment would be better protected whether it is an enterprise or a single computer. This is not the case.  In fact, many studies show computer related intrusions are on the rise. Nation state threats, advanced persistent threats (APT) and even less skilled hackers continue to improve their sophistication as tools get cheaper and information is freely exchanged. Why is it then that I say, Proactive defenses are essentially free? And if that is in fact the case, why is this not being used more frequently? Proactive defense measures are essentially free, minus the time and effort in securing the root problems within your network. For this particular blog post, I am focused on host based proactive defensive measures.

Denying Execution at the Directory Level
The "how" is actually quite simple to explain, and in fact it is not a new protection technique at all, its just not as widely used outside of *nix based systems. All that an operating system provides is a platform for applications to run on, sometimes graphical based, sometimes a simple command line. The applications are typically stored in a common location within the operating system, allowing for dynamic linking as well as simplifying the directory structure. Not all applications require the need for linking to a dynamic library as they contain all of the requirements to run on their own, so they can easily be placed anywhere within the OS and they will execute.

This is extremely convenient when a developer wants to provide software that doesn't need to officially "install", and can be easily moved around. Therein lies the issue with the execution of these "self contained" applications, they can execute from anywhere on the host, without restriction. For a demonstration of this, copy "calc.exe" from the "system32" folder on your Windows PC to your "desktop". The program "calc.exe" will execute just the same as if it were under "system32" as it is a completely self contained binary. Almost all malware is designed the same way, and typically executes from a "temp" location or the root of your currently logged in user directory. The execution of malware needs to be stopped from occurring in the first place. This way, regardless of your current AV signatures or HIDS/HIPS capabilities, the malware cannot run. If the malware is unable to run, the threat is effectively mitigated before it can gain any foothold.

So how on earth do you stop the malware from executing from within these locations, and do I need some kind of "agent" based solution to monitor those particular directories to stop them? The approach is simple: deny ALL execution of programs outside of a particular directory (e.g., "Program Files" and "System32"). Require all necessary applications on the host, putty for instance, to be placed within one of the approved directories. If you are running a Windows based environment, locking down execution outside of approved directories can be implemented through both Group Policy (GPO) and Local Policy.

By expanding on an existing Windows policy called "Microsoft Windows Software Restriction" (which has been around since 2002 BTW) you can define directories that allow for execution of applications. This exact same technique can be employed on OSX systems as well.  Simply remove the execute privilege from locations within the OS that you would like to protect. In fact, I would venture to say it is easiest to implement on any *nix based system (if it's not already, as is the case on most unix/linux flavors).

No Silver Bullet
No solution is 100% effective, and this is no exception, as there are a number of ways to get past this protection.  Having said that, it adds a layer to your defense and will stop the majority of execution-based attacks.  If your software is properly patched (0-days not included), you have user privileges locked down with separate dedicated accounts, directory protection just steps up the difficulty your attackers have in gaining a presence on your network. No single solution will solve all of your problems, no matter how much a vendor sales engineer tries to sell you. Holistic, full spectrum defenses are the future, not "plug & play" protection hardware or software that requires updates, patching, signatures and "threat intelligence". The other side extremely important level of protection is in your Infosec professionals you have supporting you. Spend the money on good, talented and well rounded security professionals that understand the cyber threat landscape and the ways in which they can help better protect your organization.

To research further into how your network and its assets can be better protected please check out CyberSquared for solutions to root cause issues.

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