Contributor:
James.Maude
May 1st, 2015

File less fears

Last week I was talking to a customer about whitelisting policies. Having rolled out least privilege, application control and sandboxing to their estate they had gone from hundreds of security incidents per week to virtually none. This has caused the security team to become more proactive by shifting from constant firefighting and reacting to incidents to thinking strategically and planning ahead.

During the conversation they raised file less malware, asking how you can defend against malware such as Poweliks that avoids dropping files on disk and hides from AV detection. Although at first this kind of threat seems highly advanced it is entirely possible to contain and block the attack using Defendpoint’s unique approach to endpoint security.

The problem

Since the popular Angler Exploit Kit started delivering Poweliks file less malware in late 2014 malware authors have been turning to this technique to bypass detection and infect systems. We are increasingly seeing native Windows tools such as PowerShell and Microsoft CryptoAPI being used by a wide variety of malware to infect, encrypt and exploit systems.

The problem with prevention is twofold – first, traditional defenses are focused for threats on disk not in memory, and second if malware uses legitimate tools such as PowerShell then it is hard to detect and distinguish from legitimate user activity. Perimeter and network defenses can reduce the amount of malicious content reaching the endpoint however it only takes one threat to bypass these to inflict damage, as such protection should start from the endpoint and work out.

The fix

As this file less malware attempts to exploit native Windows tools such as PowerShell the simplest solution is to block these tools from running using application control. This however could have a negative effect on the user, preventing them using these tools legitimately. Fortunately Defendpoint has a unique solution to this problem, whitelisting within the sandbox.

Sandboxing is one of the most effective defenses against web based malware allowing vulnerable web facing applications to be isolated from the user account. When Sandboxing is combined with context aware whitelisting the file less malware can be blocked from accessing PowerShell within the Sandbox without limiting the users access to the tool.

As the majority of threats come from the web, being able to implement a secure locked down whitelist that can distinguish between native user activity and potentially dangerous web content is a powerful weapon.

Summary

File less malware is often used to “test the water” as the first stage of an attack, it provides the ideal opportunity for an attacker to profile a system before dropping and executing the main payload on disk. Unfortunately file based detection tools such as AV are increasingly ineffective, detecting less than 50% of malware leading to long term compromise of systems.

Many vendors will struggle to counter file less malware by extending their detection engines to scan the system memory. This will suffer from the same failings as traditional AV by relying on detecting known bad behaviour when faced with unknown threats. The more proactive approach is to provide isolation and containment of unknown threats using defense in depth strategies to limit access to the system, user data and prevent malicious content from executing.

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