Analysis by: Adrian Cofreros
ALIASES:

Trojan-Dropper.Win32.Daws.bwbm (Kaspersky), Backdoor.Win32.Zegost (Ikarus), Trojan:Win32/Malagent (Microsoft), Backdoor.Sykipot (Norton), Trojan.Win32.Redosdru.C (v) (Sunbelt)

 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

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 commands from a remote malicious user, effectively compromising the affected system.

  TECHNICAL DETAILS

File Size: Varies
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 24 Apr 2014

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%\ Helper.exe - with just different size of overlay
  • %Windows%\Helper.exe - with just different size of overlay

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

Its DLL component is injected to the following process(es):

  • winlogon.exe

It adds the following mutexes to ensure that only one of its copies runs at any one time:

  • Wolf_Server_Main 1.0
  • Wolf_Server_Shield 1.0

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
Helper.exe = "%Windows%\Helper.exe"

Other System Modifications

This backdoor adds the following registry entries:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\policies\
system
ConsentPromptBehaviorAdmin = "0"

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\policies\
system
EnableLUA = "0"

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\policies\
system
PromptOnSecureDesktop = "0"

Backdoor Routine

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

  • Downloads a file
  • Executes a file
  • Creates the following registry key and adds the entry HKEY_CURRENT_USER\NetSubKey
  • Deletes the file %System%\syslog.dat
  • Connects to other remote sites, downloads, sends and receives data

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

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

  • {BLOCKED}o.{BLOCKED}7w.com:7001

Other Details

This backdoor drops the following file(s)/component(s):

  • %User Temp%\Protected.cpp
  • %Windows%\KernelSoft.dll
  • %Temp%\Protected.cpp

(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, or C:\Users\{user name}\AppData\Local\Temp on Windows Vista and 7.. %Windows% is the Windows folder, which is usually C:\Windows.. %Temp% is the Windows Temporary folder, which is usually C:\Windows\Temp.)

NOTES:

Its injected .DLL component serves as a watchdog on the process, files, and the registry.

  SOLUTION

Minimum Scan Engine: 9.700

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_CURRENT_USER
    • NetSubKey

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\CurrentVersion\Run
    • Helper.exe = "%Windows%\Helper.exe"
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\policies\system
    • ConsentPromptBehaviorAdmin = "0"
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\policies\system
    • EnableLUA = "0"
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\policies\system
    • PromptOnSecureDesktop = "0"

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.
  • %User Temp%\Protected.cpp
  • %Windows%\KernelSoft.dll
  • %Temp%\Protected.cpp

Step 6

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