DLL preloading: Making malware detection more difficult

DLL preloading makes malware detection difficult. Effective enterprise mitigation requires antimalware, Microsoft FixIt, and keeping programs current.

The PoisonIvy malware is now utilizing a technique called DLL preloading to avoid detection. Can you describe how DLL preloading works and provide some mitigation options for enterprises?

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DLL preloading, also known as binary planting, was first reported about three years ago. This technique exploits the insecure configuration in Windows for searching the current working directory for dynamic link libraries (DLLs) used within legitimate files.

Recently, Trend Micro Inc. documented that the PoisonIvy malware utilizes DLL preloading to bypass antimalware utilities. PoisonIvy also injects malicious code into a copy of Internet Explorer (iexplore.exe) running in the background to communicate over the network while bypassing firewalls.

PoisonIvy incorporated these new features to evade antimalware tools and to make the initial infection file look more legitimate. A user might assume the file, which could be masked as a Microsoft Word or Adobe Flash file, is safe and open it, allowing the file to load malware into the current working directory and execute it.

Unfortunately, not much has changed in the years since this attack was disclosed, but the learned functionality of the malware might provide some additional insight into the development practices of the malware authors. If malware authors prioritize new functionality based on requests from attackers or the impact of the new functionality, it might suggest making the attack reliable or effective -- or even including it at all -- was a lower overall priority.

To protect your enterprise from both the malware and attacks using the malware, DLL preloading mitigation steps should be taken, such as applying Microsoft FixIt and using the most recent versions of installed programs. These steps will help to minimize the chance of malicious DLLs being loaded. In addition, endpoint and network antimalware tools can also protect against PoisonIvy.  

This was last published in December 2013

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