Modified by: Rika Joi Gregorio
ALIASES:

Backdoor:Win32/PcClient.CL(Microsoft), Trojan win32:doslegacy/PCClient.LYT(Eset), Backdoor.Pcclient(Symantec)

 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:

  • 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.

It deletes itself after execution.

  TECHNICAL DETAILS

File Size: 62,608 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 17 Oct 2013

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 files:

  • %System%\0004f5f7.sys
  • %System%\{random 5 letters}.dll

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

Autostart Technique

This backdoor registers its dropped component as a system service to ensure its automatic execution at every system startup. It does this by creating the following registry entries:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\MSDTCSERVEsss
ImagePath = "%System%\svchost.exe -k MSDTCSERVEsss"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\MSDTCSERVEsss
DisplayName = "Distributed Tracking Servess"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\MSDTCSERVEsss\Parameters
ServiceDll = "%System%\{random 5 letters}.dll"

It registers its dropped component as a system service to ensure its automatic execution at every system startup. It does this by creating the following registry keys:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\MSDTCSERVEsss

Other System Modifications

This backdoor adds the following registry entries:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\SvcHost
MSDTCSERVEsss = "MSDTCSERVEsss"

Other Details

This backdoor connects to the following possibly malicious URL:

  • {BLOCKED}y.{BLOCKED}u.com
  • {BLOCKED}y.{BLOCKED}u.com

It deletes itself after execution.

  SOLUTION

Minimum Scan Engine: 9.300
VSAPI OPR PATTERN File: 7.541.00
VSAPI OPR PATTERN Date: 15 Oct 2010

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 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\SYSTEM\CurrentControlSet\Services
    • MSDTCSERVEsss

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\SOFTWARE\Microsoft\Windows NT\CurrentVersion\SvcHost
    • MSDTCSERVEsss = "MSDTCSERVEsss"

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.
  • %System%\0004f5f7.sys
  • %System%\{random 5 letters}.dll

Step 6

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