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BKDR_XTRAT.NT

October 16, 2012
 Analysis by: Rhena Inocencio
 ALIASES:

Backdoor:Win32/Xtrat.A (Microsoft), Trojan.Gen (Symantec), Win32/Remtasu.F trojan (ESET), W32/Remtasu.F (Fortinet)

 PLATFORM:

Windows 2000, Windows XP, Windows Server 2003

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

  • 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.

  TECHNICAL DETAILS

File Size:

1,314,816 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

11 Oct 2012

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 copies of itself into the affected system:

  • %Windows%\App\winlog.exe

(Note: %Windows% is the Windows folder, which is usually C:\Windows or C:\WINNT.)

It injects itself into the following processes as part of its memory residency routine:

  • iexplorer.exe
  • svchost.exe

Autostart Technique

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

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Run
NetUser = "%Windows%\App\winlog.exe"

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
Netlow = "%Windows%\App\winlog.exe"

Other System Modifications

This backdoor adds the following registry keys:

HKEY_CURRENT_USER\Software\XtremeRAT

HKEY_CURRENT_USER\Software\Hat4peBdnc18C98x

It adds the following registry entries:

HKEY_CURRENT_USER\Software\XtremeRAT
Mutex = "Hat4peBdnc18C98x"

HKEY_CURRENT_USER\Software\Hat4peBdnc18C98x
ServerStarted = "{Date and Time}"

HKEY_CURRENT_USER\Software\Hat4peBdnc18C98x
ServerName = "%Windows%\App\winlog.exe"

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Active Setup\Installed Components\{GUID}
StubPath = "%Windows%\App\winlog.exe restart"

  SOLUTION

Minimum Scan Engine:

9.200

FIRST VSAPI PATTERN FILE:

9.454.02

FIRST VSAPI PATTERN DATE:

11 Oct 2012

VSAPI OPR PATTERN File:

9.455.00

VSAPI OPR PATTERN Date:

12 Oct 2012

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 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\CurrentVersion\Run
    • NetUser = "%Windows%\App\winlog.exe"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
    • Netlow = "%Windows%\App\winlog.exe"
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Active Setup\Installed Components\{GUID}
    • StubPath = "%Windows%\App\winlog.exe restart"

Step 4

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_CURRENT_USER\Software
    • XtremeRAT
  • In HKEY_CURRENT_USER\Software
    • Hat4peBdnc18C98x

Step 5

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