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Sandbox evasion: How to detect cloaked malware

Cloaked malware, like DGA.Changer, can reportedly evade sandbox detection. Nick Lewis explains how to handle the risk.

Certain types of malware, including the recent DGA.Changer, has been said to have a cloaking property that allows it to evade sandboxes. Can you please explain what cloaked malware really is and how it is able to avoid sandboxes? What other security measures should my enterprise put in place beyond sandboxing to detect cloaked malware?

Malware using domain-generation algorithms (DGAs) to identify the command-and-control (C&C) infrastructure has emerged over the last year. A recent blog post from Seculert reported that the DGA.Changer malware is just a downloader that installs other malware that will be used to further infect the system. However, one unique feature of DGA.Changer is the cloaking method it uses to evade detection and slow malware analysis: It can receive commands from its C&C to change the DGA "seed" it uses to create random domains.

Let me explain. When an algorithm generates the same domain names on all systems, that can be detected by a sandbox and quarantined as suspicious based on an established pattern. If it changes its seed on demand, it cannot be detected and may bypass the sandbox altogether because the malware is suddenly not communicating with any of the known-bad domains.

Enterprises can detect malware using DGA by monitoring DNS requests and looking for systems that perform lookups on nonexistent domain names or ones that are highly unusual (never before accessed from the domain). The malware could also be detected by a network-based antimalware appliance or by monitoring DNS logs for failed lookups. An endpoint looking up an abnormal number of domains in a short period of time should also be investigated to determine if the endpoint was compromised.

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This was last published in July 2014

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