Analysis by: Andrei Castillo
ALIASES:

Trojan horse Generic27.BTZY(AVG), W32/Buzus.AABA!tr(Fortinet), Trojan.Win32.Jorik(Ikarus), Trojan.Win32.Slenfbot.tw(Kaspersky), Backdoor:Win32/Tofsee.F(Microsoft), Trojan-FACW!7557A1FD9E4B(NAI), Win32/Injector.PUH trojan(NOD32), Trojan.Win32.Generic!BT(Sunbelt), Trojan.Jorik.IRCbot(VBA32), TR/Patched.Ren.Gen(Antivir)

 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:
 INFORMATION EXPOSURE:

  • Threat Type: Backdoor

  • Destructiveness: No

  • Encrypted: Yes

  • In the wild: Yes

  OVERVIEW

Infection Channel: Downloaded from the Internet, Dropped by other malware

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.

It does not have any information-stealing capability.

  TECHNICAL DETAILS

Ports: TCP Port 80 (HTTP), Port 25 (Simple Mail Transfer)
File Size: 619,008 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 11 Oct 2013
Payload: Compromises system security, Connects to URLs/IPs, Drops files

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 and executes the following files:

  • %User Temp%\{random number}.bat

(Note: %User Temp% is the current user's Temp folder, which is usually C:\Documents and Settings\{user name}\Local Settings\Temp on Windows 2000, XP, and Server 2003, or C:\Users\{user name}\AppData\Local\Temp on Windows Vista and 7.)

It drops the following copies of itself into the affected system:

  • %User Profile%\{random file name}.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.)

It injects codes into the following process(es):

  • %System%\svchost.exe

(Note: %System% is the Windows system folder, which is usually C:\Windows\System32.)

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
MSConfig = ""%User Profile%\{random file name}.exe" /r"

Other System Modifications

This backdoor modifies the following registry entries:

HKEY_CURRENT_USER\Software\Microsoft\
CurrentVersion\Internet Settings\ZoneMap
ProxyBypass = "1"

(Note: The default value data of the said registry entry is "0".)

HKEY_CURRENT_USER\Software\Microsoft\
CurrentVersion\Internet Settings\ZoneMap
IntranetName = "1"

(Note: The default value data of the said registry entry is "0".)

HKEY_CURRENT_USER\Software\Microsoft\
CurrentVersion\Internet Settings\ZoneMap
UNCAsIntranet = "1"

(Note: The default value data of the said registry entry is "0".)

HKEY_CURRENT_USER\Software\Microsoft\
CurrentVersion\Internet Settings\ZoneMap
AutoDetect = "1"

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

Backdoor Routine

This backdoor connects to the following URL(s) to send and receive commands from a remote malicious user:

  • {BLOCKED}bgddtyh.biz
  • {BLOCKED}hbyrukl.ch

As of this writing, the said servers are currently inaccessible.

Information Theft

This backdoor does not have any information-stealing capability.

Other Details

This backdoor connects to the following URL(s) to check for an Internet connection:

  • microsoft.com
  • yahoo.com
  • google.com

NOTES:

The dropped .BAT file is executed to delete its initial copy and the .BAT file the malware created.

It creates a new process for svchost.exe into which it injects its malicious routines.

This backdoor has the capability to send or forward SMTP traffic to the mail servers of the following:

  • mxs.mail.ru
  • yahoo.com
  • google.com
  • inbound.protection.outlook.com

  SOLUTION

Minimum Scan Engine: 9.300
FIRST VSAPI PATTERN FILE: 10.334.01
FIRST VSAPI PATTERN DATE: 11 Oct 2013
VSAPI OPR PATTERN File: 10.335.00
VSAPI OPR PATTERN Date: 11 Oct 2013

Step 1

Before doing any scans, Windows XP, Windows Vista, and Windows 7 users must disable System Restore to allow full scanning of their computers.

Step 2

Restart in Safe Mode

[ Learn More ]

Step 3

Delete this registry value

[ Learn More ]

Important: Editing the Windows Registry incorrectly can lead to irreversible system malfunction. Please do this step only if you know how or you can ask assistance from your system administrator. Else, check this Microsoft article first before modifying your computer's registry.

  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
    • MSConfig = ""%User Profile%\{random file name}.exe" /r"

Step 4

Restore this modified registry value

[ Learn More ]

Important: Editing the Windows Registry incorrectly can lead to irreversible system malfunction. Please do this step only if you know how or you can ask assistance from your system administrator. Else, check this Microsoft article first before modifying your computer's registry.

  • In HKEY_CURRENT_USER\Software\Microsoft\CurrentVersion\Internet Settings\ZoneMap
    • From: ProxyBypass = "1"
      To: ProxyBypass = "0"
  • In HKEY_CURRENT_USER\Software\Microsoft\CurrentVersion\Internet Settings\ZoneMap
    • From: IntranetName = "1"
      To: IntranetName = "0"
  • In HKEY_CURRENT_USER\Software\Microsoft\CurrentVersion\Internet Settings\ZoneMap
    • From: UNCAsIntranet = "1"
      To: UNCAsIntranet = "0"
  • In HKEY_CURRENT_USER\Software\Microsoft\CurrentVersion\Internet Settings\ZoneMap
    • From: AutoDetect = "1"
      To: AutoDetect = "1" (Default), modifies if "0"

Step 5

Search and delete this file

[ Learn More ]
There may be some files that are hidden. Please make sure you check the Search Hidden Files and Folders checkbox in the "More advanced options" option to include all hidden files and folders in the search result.  
  • %User Profile%\{random file name}.exe

Step 6

Restart in normal mode and scan your computer with your Trend Micro product for files detected as BKDR_TOFSEE.MN. If the detected files have already been cleaned, deleted, or quarantined by your Trend Micro product, no further step is required. You may opt to simply delete the quarantined files. Please check this Knowledge Base page for more information.


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