BKDR_REFROSO.VTH

April 06, 2015
 Analysis by: Jaime Benigno Reyes
 ALIASES:

Trojan:Win32/Comitsproc!gmb (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.

However, as of this writing, the said sites are inaccessible.

  TECHNICAL DETAILS

File Size:

323,584 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

25 Mar 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:

  • %Start Menu%\Programs\Startup\4d70261a3fd06681c7b11c7e97039966.exe
  • %User Temp%\wendos.exe

(Note: %Start Menu% is the Start Menu folder, where it usually is C:\Documents and Settings\{user name}\Start Menu on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\AppData\Roaming\Microsoft\Windows\Start Menu 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.. %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 adds the following registry entries to enable its automatic execution at every system startup:

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
4d70261a3fd06681c7b11c7e97039966 = ""%User Temp%\wendos.exe" .."

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Run
4d70261a3fd06681c7b11c7e97039966 = ""%User Temp%\wendos.exe" .."

Other System Modifications

This backdoor adds the following registry keys:

HKEY_CURRENT_USER\Software\4d70261a3fd06681c7b11c7e97039966

It adds the following registry entries as part of its installation routine:

HKEY_CURRENT_USER\Environment
SEE_MASK_NOZONECHECKS = "1"

HKEY_CURRENT_USER\Software\Microsoft\
Windows NT\CurrentVersion\Winlogon
ParseAutoexec = "1"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
services\SharedAccess\Parameters\
FirewallPolicy\FirewallRules
{GUID} = "{version}|Action=Allow|Active=TRUE|Dir=In|Protocol={number}|Profile=Public|App=%User Temp%\wendos.exe|Name=wendos.exe|" (Windows Vista and higher versions)

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\SharedAccess\Parameters\
FirewallPolicy\StandardProfile\AuthorizedApplications\
List
%User Temp%\wendos.exe = "%User Temp%\wendos.exe:*:Enabled:wendos.exe" (Versions lower than Windows Vista)

Other Details

This backdoor connects to the following possibly malicious URL:

  • {BLOCKED}.{BLOCKED}.99.23:1177

However, as of this writing, the said sites are inaccessible.