ALIASES:

Microsoft: Horst; Symantec: Horst; Sophos: Horst; Authentium: Horst; Bitdefender: Horst; Fortinet: Horst; Fprot: Horst; Eset: Horst; VBA32: Horst

 PLATFORM:

Windows 2000, Windows Server 2003, Windows XP (32-bit, 64-bit), Windows Vista (32-bit, 64-bit), Windows 7 (32-bit, 64-bit)

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

  • Threat Type: Trojan

  • Destructiveness: No

  • Encrypted:

  • In the wild: Yes

  OVERVIEW

Infection Channel: Downloaded from the Internet

HORST variants are usually associated with MEDBOT malware as their component. HORST malware are used to convert affected systems into proxy servers. They are essentially "relay agents," and since they act as an intermediary between a client and a server, a malicious user can use the affected system to hide his actual location when executing remote commands.

  TECHNICAL DETAILS

Memory Resident: Yes
Payload: Connects to URLs/IPs, Downloads files

Installation

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

  • %Application Data%\ieudinit.exe
  • %Application Data%\sessmgr.exe
  • %System%\comrepl.exe
  • %System%\mstsc.exe
  • %User Temp%\cmstp.exe
  • %User Temp%\comrepl.exe
  • %User Temp%\esentutl.exe
  • %User Temp%\ieudinit.exe
  • %Windows%\esentutl.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.. %System% is the Windows system folder, where it usually is C:\Windows\System32 on all Windows operating system versions.. %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.. %Windows% is the Windows folder, where it usually is C:\Windows on all Windows operating system versions.)

Autostart Technique

This Trojan adds the following registry entries to enable its automatic execution at every system startup:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Run
ComRepl = "%System%\comrepl.exe /com /w"

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Policies\
Explorer\Run
SessMgr = "%Application Data%\sessmgr.exe /waitservice"

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\policies\
Explorer\Run
ComRepl = "%User Temp%\comrepl.exe /waitservice"

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Policies\
Explorer\Run
IEudinit = "%User Temp%\ieudinit.exe /waitservice"

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\policies\
Explorer\Run
Esent Utl = "%Windows%\esentutl.exe /waitservice"

It modifies the following registry entries to ensure it automatic execution at every system startup:

HKEY_CURRENT_USER\Software\Microsoft\
Windows NT\CurrentVersion\Windows
load = "%User Temp%\esentutl.exe"

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

HKEY_CURRENT_USER\Software\Microsoft\
Windows NT\CurrentVersion\Windows
load = "%Application Data%\ieudinit.exe"

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

Other System Modifications

This Trojan adds the following registry keys as part of its installation routine:

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Policies\
Explorer\Run

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\policies\
Explorer

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\policies\
Explorer\Run

Other Details

This Trojan connects to the following possibly malicious URL:

  • http://{BLOCKED}w.{BLOCKED}k.com/?&publicid=72b67aeb-32ba-4635-be5a-30d584ab8336&domainname={BLOCKED}.com
  • http://{BLOCKED}p.{BLOCKED}d.com/up/calc.bin
  • http://ww5.{BLOCKED}us.com/img/gt.cgi?s=2964510435&r=jcvd
  • http://www.{BLOCKED}um.com/img/gt.cgi?s=2964510435&r=jcce
  • http://www.{BLOCKED}us.com/img/gt.cgi?s=2964510435&r=jcvd