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.
IOCs
WinBio.dll (scrubbed key and payload) SHA256
7bdae0dfc37cb5561a89a0b337b180ac6a139250bd5247292f470830bd96dda7
c1c68454e82d79e75fefad33e5acbb496bbc3f5056dfa26aaf1f142cee1af372
Carbanak SHA256
77a6fbd4799a8468004f49f5929352336f131ad83c92484b052a2eb120ebaf9a
42d3cf75497a724e9a9323855e0051971816915fc7eb9f0426b5a23115a3bdcb
