Cyberespionage group abuses Windows hotpatching mechanism for malware stealth

A cyberespionage group active in Asia has been leveraging a Windows feature known as hotpatching in order to better hide its malware from security products.

The group, which malware researchers from Microsoft call Platinum, has been active since at least 2009 and has primarily targeted government organizations, defense institutes, intelligence agencies and telecommunications providers in South and Southeast Asia, especially from Malaysia, Indonesia and China.

So far the group has used spear phishing — fraudulent emails that target specific organizations or individuals — as its main attack method, often combining it with exploits for previously unknown, or zero-day, vulnerabilities that install custom malware. It places great importance on remaining undetected.

To achieve this, it only launches a small number of attack campaigns every year. Its custom malware components have self-deletion capabilities and are designed to run only during the victims’ working hours, to hide their activity among regular user traffic, Microsoft’s Windows Defender Advanced Threat Hunting team said in a report.

While the Microsoft researchers stopped short of saying with certainty that Platinum is a state-sponsored cyberespionage group, they said that “the group shows traits of being well funded, organized, and focused on information that would be of most use to government bodies.”

One of the more interesting techniques used by the group is known as hotpatching. This leverages a somewhat obscure feature that was first introduced in Windows Server 2003 and which allows the dynamic updating of system components without the need to reboot the computer.

Hotpatching was removed in Windows 8 and later versions, because it was rarely used. During the 12 years support life of Windows Server 2003, only 10 patches used this technique.

The potential use of hotpatching as a stealth way to inject malicious code into running processes was described by security researcher Alex Ionescu at the SyScan security conference in 2013. And it is his technique that the Platinum group uses.

This is the first time that the Microsoft researchers have seen the technique used in the wild by malicious attackers.

“Using hotpatching in a malicious context is a technique that can be used to avoid being detected, as many antimalware solutions monitor non-system processes for regular injection methods, such as CreateRemoteThread,” the Microsoft researchers said in a blog post. “What this means in practical terms is that PLATINUM was able to abuse this feature to hide their backdoor from the behavioral sensors of many host security products.”