Researchers observed a new tool attributed to the FIN7 hacker group dubbed BIOLOAD aimed to minimize the footprint in the victim machine and to avoid detection.
The new tool has similarities with FIN7’s BOOSTWRITE tool that abuses the DLL search order of applications to get executed. BOOSTWRITE abuses legitimate ‘Dwrite.dll’ provided by the Microsoft DirectX Typography Services.
FIN7 New Tool
BIOLOAD is the new version of the BOOSTWRITE tool, both of them having the same codebase and drops the Carbanak backdoor. Both the tools taking advantage of the Windows OS method to look for required DLLs to load into a program.
The BIOLOAD tool abuses FaceFodUninstaller.exe (“%WINDR%\System32\WinBioPlugIns”) that exist with the Windows OS installation and this executable depends on the winbio.dll (“%WINDR%\System32”). The FaceFodUninstaller has a built-in scheduled task which grabs attackers’ interest to target this executable.
Attackers leverage the default DLL search order by placing the fake version of WinBio.dll(contains upper case letters) int he same folder of FaceFodUninstaller “%WINDR%\System32\WinBioPlugIns”, to place the “attacker needed to have elevated privileges on the victim’s machine such as an administrator or a SYSTEM account,” reads Fortinet blog post.
BIOLOAD was written in C++, compiled in March and July of 2019, it specifically targets 64-bit OS machines. It has an encrypted payload embedded like BOOSTWRITE, for decryption it uses XOR algorithm or fetches. Like BOOSTWRITE, BIOLOAD also supports only a single payload.
The loader carries the newly built version of the Carbanak Backdoor, dated January and April of 2019, according to their timestamps.
Researchers noted that backdoor “checks to see if another Anti-Virus (AV) is running on the machine, besides Kaspersky, AVG, and TrendMicro. The result, however, does not affect the operations of the backdoor, unlike with previously detected AVs.”
FIN7 hacker group found to be active since mid-2015, the group continues adding new tools to their arsenal to defeat security solutions.
Both the BIOLOAD and the new version of Carbanak remain undetected by most of the AV engines, here are the results from the virus total 1,2 at the time of writing.
WinBio.dll (scrubbed key and payload) SHA256