Analysis by: Mark Joseph Manahan
ALIASES:

Trojan.Win32.Samsa.b (Kaspersky), Trojan:Win32/Enfal.C (Microsoft), Backdoor.Samkams!gen2 (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:

  • 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 executes then deletes itself afterward.

  TECHNICAL DETAILS

File Size: 65,586 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 04 Jan 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 copies of itself into the affected system:

  • %System%\DisMngt.exe
  • %System%\Winkrnl.exe

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

It executes then deletes itself afterward.

Autostart Technique

This backdoor modifies the following registry entries to ensure it automatic execution at every system startup:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\Winlogon
Userinit = "%System%\userinit.exe,%System%\DisMgnt.exe"

(Note: The default value data of the said registry entry is %System%\userinit.exe,.)

Other Details

This backdoor connects to the following possibly malicious URL:

  • www.{BLOCKED}s.com

  SOLUTION

Minimum Scan Engine: 9.300
FIRST VSAPI PATTERN FILE: 9.636.03
FIRST VSAPI PATTERN DATE: 04 Jan 2013
VSAPI OPR PATTERN File: 9.637.00
VSAPI OPR PATTERN Date: 05 Jan 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

Restore these modified registry values

[ Learn More ]

Important:Editing the Windows Registry incorrectly can lead to irreversible system malfunction. Please do this only if you know how to or you can seek your system administrator's help. You may also check out this Microsoft article first before modifying your computer's registry.

  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon
    • From: Userinit = "%System%\userinit.exe,%System%\DisMngt.exe"
      To: Userinit = "%System%\userinit.exe,"

Step 4

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