TROJ_DROPPER.FVZ

 Analysis by: Christopher Daniel So

 ALIASES:

TrojanDropper:Win32/Zegost.B (Microsoft), Trojan.Gen (Symantec), Generic Dropper!dht (McAfee), Trojan.Win32.Agent.ddpg (Kaspersky)

 PLATFORM:

Windows 2000, XP, Server 2003

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

  • 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.

It connects to certain URLs. It may do this to remotely inform a malicious user of its installation. It may also do this to download possibly malicious files onto the computer, which puts the computer at a greater risk of infection by other threats.

  TECHNICAL DETAILS

File Size:

105609 bytes

File Type:

PE

Memory Resident:

Yes

Initial Samples Received Date:

06 Mar 2007

Payload:

Drops files, Connects to URLs/Ips

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 files:

  • %System Root%\Documents and Settings\All Users\Application Data\Storm\update\%SESSIONNAME%\cenmu.cc3
  • %User Temp%\hsrccexskf.dat
  • %System%\e22a4301.rdb

(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.. %System% is the Windows system folder, which is usually C:\Windows\System on Windows 98 and ME, C:\WINNT\System32 on Windows NT and 2000, or C:\Windows\System32 on Windows XP and Server 2003.)

It creates the following folders:

  • %System Root%\Documents and Settings\All Users\Application Data\Storm\update\%SESSIONNAME%

Autostart Technique

This Trojan registers itself as a system service to ensure its automatic execution at every system startup by adding the following registry entries:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Commessenger70
Type = "20"

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Commessenger70
Start = "2"

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Commessenger70
ErrorControl = "0"

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Commessenger70
ImagePath = "%SystemRoot%\system32\svchost.exe -k netsvcs"

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Commessenger70
DisplayName = "Messenger"

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Commessenger70
ObjectName = "LocalSystem"

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Commessenger70
Description = "Transmits net send and Alerter service messages between clients and servers. This service is not related to Windows Messenger. If this service is stopped, Alerter messages will not be transmitted. If this service is disabled, any services that explicitly depend on it will fail to start."

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Commessenger70\Parameters
seRVicemAIN = "BuildTrusteeWithSidA"

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Commessenger70\Parameters
seRVicedlL = "%System Root%\Documents and Settings\All Users\Application Data\Storm\update\%SESSIONNAME%\cenmu.cc3"

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Commessenger70\Parameters
module = "%System Root%\cubxdjsupj"

It registers as a system service to ensure its automatic execution at every system startup by adding the following registry keys:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Commessenger70

Other System Modifications

This Trojan adds the following registry entries:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\Messenger
FailureActions = "{random values}"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\Messenger
Group = ""

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\Messenger\Parameters
seRVicemAIN = "BuildTrusteeWithSidA"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\Messenger\Parameters
module = "%System Root%\cubxdjsupj"

It modifies the following registry entries:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\Messenger
Start = "2"

(Note: The default value data of the said registry entry is 4.)

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\Messenger
ErrorControl = "0"

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

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\Messenger\Parameters
ServiceDll = "%System Root%\Documents and Settings\All Users\Application Data\Storm\update\%SESSIONNAME%\cenmu.cc3"

(Note: The default value data of the said registry entry is %SystemRoot%\System32\msgsvc.dll.)

Download Routine

This Trojan connects to the following malicious URLs:

  • {BLOCKED}14.3322.org:18188

  SOLUTION

Minimum Scan Engine:

8.900

FIRST VSAPI PATTERN FILE:

4.326.01

FIRST VSAPI PATTERN DATE:

08 Mar 2007

Step 1

For Windows XP and Windows Server 2003 users, before doing any scans, please make sure you disable System Restore to allow full scanning of your computer.

Step 2

Restart in Safe Mode

[ Learn More ]

Step 3

Delete this registry key

[ 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_LOCAL_MACHINE\SOFTWARE\Microsoft
    • Commessenger70

Step 4

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_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Messenger
    • FailureActions = "{random values}"
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Messenger
    • Group = ""
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Messenger\Parameters
    • seRVicemAIN = "BuildTrusteeWithSidA"
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Messenger\Parameters
    • module = "%System Root%\cubxdjsupj"

Step 5

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_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Messenger
    • From: Start = "2"
      To: Start = "4"
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Messenger
    • From: ErrorControl = "0"
      To: ErrorControl = "1"
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Messenger\Parameters
    • From: ServiceDll = "%System Root%\Documents and Settings\All Users\Application Data\Storm\update\%SESSIONNAME%\cenmu.cc3"
      To: ServiceDll = "%SystemRoot%\System32\msgsvc.dll"

Step 6

Search and delete this folder

[ Learn More ]
Please make sure you check the Search Hidden Files and Folders checkbox in the More advanced options option to include all hidden folders in the search result. %System Root%\Documents and Settings\All Users\Application Data\Storm\update\%SESSIONNAME%

Step 7

Search and delete these files

[ Learn More ]
There may be some component 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 Temp%\hsrccexskf.dat
%System%\e22a4301.rdb

Step 8

Restart in normal mode and scan your computer with your Trend Micro product for files detected as TROJ_DROPPER.FVZ. 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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