Analysis by: Ardin Christopher Maglalang
ALIASES:

W32/DLDER.CZ3!tr(Fortinet)

 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: No

  • 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.

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

  TECHNICAL DETAILS

File Size: 11,264 bytes
File Type: EXE
Memory Resident: No
Payload: Compromises system security, Connects to URLs/IPs

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.

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
DriverCache = "{Malware path and filename}"

Backdoor Routine

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

  • http://www.{BLOCKED}sten.com/help.html

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

NOTES:

This backdoor executes the following commands from a remote malicious user:

  • run1 - used to remotely execute shell commands from http://www.{BLOCKED}ofthomes.com/updateinfo.html
  • run2 - used to remotely execute shell commands from http://www.{BLOCKED}sten.com/updateinfo.html
  • run3 - used to remotely execute shell commands from http://www.{BLOCKED}t.net/updateinfo.html
  • http: - used to remotely execute shell commands from the URL specified by malicious remote user
  • Http: - download and execute arbitrary file from a URL specified by the remote user
  • x_ - sleep\idle for a span of time specified by malicious user

It saves the file it downloads using the following name:

  • %User Temp%\~DF20.tmp

  SOLUTION

Minimum Scan Engine: 9.700
FIRST VSAPI PATTERN FILE: 10.630.06

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

Scan your computer with your Trend Micro product and note files detected as BKDR_SLOTH.A

Step 3

Terminate a process file/s detected as BKDR_SLOTH.A

[ Learn More ]

*Note: If the detected file/s is/are not displayed in theWindows Task Manager, continue doing the next steps.

Step 4

Delete the registry entry with an unknown data 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.

 
  • HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run

Step 5

Scan your computer with your Trend Micro product to delete files detected as BKDR_SLOTH.A. 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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