BKDR_FYNLOSKI.SADR

October 03, 2015
 Analysis by: Homer Pacag
 ALIASES:

Backdoor:Win32/Fynloski.A (Microsoft)

 PLATFORM:

Windows

 OVERALL RISK RATING:
 DAMAGE POTENTIAL:
 DISTRIBUTION POTENTIAL:
 REPORTED INFECTION:
 INFORMATION EXPOSURE:

  • Threat Type: Backdoor

  • Destructiveness: No

  • Encrypted:

  • In the wild: Yes

  OVERVIEW

This backdoor arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.

  TECHNICAL DETAILS

File Size:

573,952 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

02 Oct 2015

Arrival Details

This backdoor arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.

Installation

This backdoor drops the following copies of itself into the affected system and executes them:

  • %User Profile%\My Documents\MSDCSC\msdcsc.exe
  • %User Temp%\MC CRACKED.EXE

(Note: %User Profile% is the current user's profile folder, which is usually C:\Documents and Settings\{user name} on Windows 2000, XP, and Server 2003, or C:\Users\{user name} on Windows Vista and 7.. %User Temp% is the user's temporary folder, where it usually is C:\Documents and Settings\{user name}\Local Settings\Temp on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\AppData\Local\Temp on Windows Vista (32- and 64-bit), Windows 7 (32- and 64-bit), Windows 8 (32- and 64-bit), Windows 8.1 (32- and 64-bit), Windows Server 2008, and Windows Server 2012.)

It drops the following component file(s):

  • %User Temp%\e4jD.tmp_dir\exe4jlib.jar
  • %User Temp%\e4jD.tmp_dir\i4jdel.exe
  • %User Temp%\e4jD.tmp_dir\MinecraftSP.jar
  • %User Temp%\e4jE.tmp_dir\exe4jlib.jar
  • %User Temp%\e4jE.tmp_dir\i4jdel.exe
  • %User Temp%\e4jE.tmp_dir\MinecraftSP.jar
  • %User Temp%\e4jF.tmp_dir\exe4jlib.jar
  • %User Temp%\e4jF.tmp_dir\i4jdel.exe;
  • %User Temp%\e4jF.tmp_dir\MinecraftSP.jar
  • %User Temp%\dclogs\{YYYY-MM-DD-S}.dc

(Note: %User Temp% is the user's temporary folder, where it usually is C:\Documents and Settings\{user name}\Local Settings\Temp on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\AppData\Local\Temp on Windows Vista (32- and 64-bit), Windows 7 (32- and 64-bit), Windows 8 (32- and 64-bit), Windows 8.1 (32- and 64-bit), Windows Server 2008, and Windows Server 2012.)

It creates the following folders:

  • %User Profile%\My Documents\MSDCSC
  • %User Temp%\e4jD.tmp_dir
  • %User Temp%\e4jE.tmp_dir
  • %User Temp%\e4jF.tmp_dir
  • %User Temp%\dclogs\

(Note: %User Profile% is the current user's profile folder, which is usually C:\Documents and Settings\{user name} on Windows 2000, XP, and Server 2003, or C:\Users\{user name} on Windows Vista and 7.. %User Temp% is the user's temporary folder, where it usually is C:\Documents and Settings\{user name}\Local Settings\Temp on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\AppData\Local\Temp on Windows Vista (32- and 64-bit), Windows 7 (32- and 64-bit), Windows 8 (32- and 64-bit), Windows 8.1 (32- and 64-bit), Windows Server 2008, and Windows Server 2012.)

Autostart Technique

This backdoor creates the following registry entries to enable automatic execution of dropped component at every system startup:

HKCU\Software\Microsoft\
Windows\CurrentVersion\Run
MicroUpdate = %User Profile%\My Documents\My Documents\MSDCSC\msdcsc.exe

HKLM\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\Winlogon
UserInit = %System%\userinit.exe,%User Profile%\My Documents\MSDCSC\msdcsc.exe

Other System Modifications

This backdoor adds the following registry keys:

HKCU\Software\DC3_FEXEC

Other Details

This backdoor connects to the following possibly malicious URL:

  • {BLOCKED}.{BLOCKED}.155.100