Analysis by: Mar Philip Elaurza
ALIASES:

Worm:Win32/Folstart!rfn (Microsoft); Worm:Win32/Folstart!rfn (Symantec);

 PLATFORM:

Windows

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

  • Threat Type: Trojan

  • Destructiveness: No

  • Encrypted:

  • In the wild: Yes

  OVERVIEW

This Trojan 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: 3,325,952 bytes
File Type: EXE
Initial Samples Received Date: 27 Nov 2015

Arrival Details

This Trojan 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 Trojan drops the following copies of itself into the affected system:

  • %Application Data%\Start\update.exe
  • {Removable Drive Letter}:\{Folder Name in the Removable Drive}.exe

(Note: %Application Data% is the Application Data folder, where it usually is C:\Documents and Settings\{user name}\Application Data on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\AppData\Roaming 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:

  • %Application Data%\S-1-5-31-1286970278978-5713669491-166975984-320
  • %Application Data%\S-1-5-31-1286970278978-5713669491-166975984-320\dmc
  • %Application Data%\S-1-5-31-1286970278978-5713669491-166975984-320\tlsr
  • %Application Data%\S-1-5-31-1286970278978-5713669491-166975984-320\Rotinom
  • %Application Data%\Start
  • {Malware Path}\{Malware Filename}
  • {Removable Drive Letter}:\Usb 2.0 Driver
  • {Removable Drive Letter}:\Usb 2.0 Driver\S-1-5-31-1286970278978-5713669491-166975984-320
  • {Removable Drive Letter}:\Usb 2.0 Driver\S-1-5-31-1286970278978-5713669491-166975984-320\dmc
  • {Removable Drive Letter}:\Usb 2.0 Driver\S-1-5-31-1286970278978-5713669491-166975984-320\tlsr

(Note: %Application Data% is the Application Data folder, where it usually is C:\Documents and Settings\{user name}\Application Data on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\AppData\Roaming 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.)

Other System Modifications

This Trojan adds the following registry entries:

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Explorer\
Advanced
ShowSuperHidden = "0"

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Explorer\
Advanced
WebViewBarricade = "0"

It modifies the following registry entries:

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Explorer\
Advanced
Hidden = "2"

(Note: The default value data of the said registry entry is 2.)

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Explorer\
Advanced
HideFileExt = "1"

(Note: The default value data of the said registry entry is 1.)

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Explorer\
Shell Folders
Startup = "%Application Data%\Start"

(Note: The default value data of the said registry entry is %User Profile%\Start Menu\Programs\Startup.)

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Explorer\
User Shell Folders
Startup = "%Application Data%\Start"

(Note: The default value data of the said registry entry is {random values}.)