The LockPoS Point-of-Sale (PoS) malware has been leveraging a new code injection technique to compromise systems, Cyberbit researchers say.

First detailed in July this year, LockPoS steals credit card data from the memory of computers attached to PoS credit card scanners. The malware was designed to read the memory of running processes and collect credit card data that is then sent to its command and control (C&C) server.

Previous analysis revealed that the threat used a dropper that injects it directly into the explorer.exe process. After execution, the dropper extracts a resource file from itself and injects various components that load the final LockPoS payload.

The malware is now employing an injection method that appears to be a new variant of a technique previously employed by the Flokibot PoS malware. With LockPoS distributed from the Flokibot botnet, and with the two threats sharing similarities, this doesn’t come as a surprise.

One of the injection techniques employed by LockPoS involves creating a section object in the kernel, calling a function to map a view of that section into another process, then copying code into the section and creating a remote thread to execute the mapped code, Cyberbit says.

LockPoS was observed using 3 main routines to inject code into a remote process, namely NtCreateSection, NtMapViewOfSection, and NtCreateThreadEx, all three exported from ntdll.dll, a core Dynamic-link library (DLL) file in the Windows operating system.

Instead of calling said routines, the malware maps ntdll.dll from the disk to its own virtual address space, which allows it to maintain a “clean” copy of the DLL file. LockPoS also allocates a buffer for saving the system calls number, copies malicious code to the shared mapped section, then creates a remote thread in explorer.exe to execute its malicious code.

By using this “silent” malware injection method, the malware can avoid any hooks that anti-malware software might have installed on ntdll.dll, thus increasing the chances of a successful attack.

“This new malware injection technique suggests a new trend could be developing of using old sequences in a new way that makes detection difficult,” Hod Gavriel, malware analyst at Cyberbit, explains.

While most endpoint detection and response (EDR) and next-gen antivirus products already monitor the Windows functions in user mode, kernel functions can’t be monitored in Windows 10, where the kernel space is still guarded. To ensure successful detection, improved memory analysis should be employed, the researcher says.

Related: LockPoS Point of Sale Malware Emerges

Related: Targeted FlokiBot Attacks Hit PoS Systems in Brazil