Analysis by: Erika Bianca Mendoza
 PLATFORM:

Windows 2000, Windows XP, Windows Server 2003

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

  • Threat Type: Backdoor

  • Destructiveness: No

  • Encrypted: No

  • In the wild: Yes

  OVERVIEW

This backdoor may be unknowingly downloaded by a user while visiting malicious websites.

  TECHNICAL DETAILS

File Size: 774,144 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 02 Nov 2011
Payload: Connects to URLs/IPs

Arrival Details

This backdoor may be unknowingly downloaded by a user while visiting malicious websites.

Installation

This backdoor drops the following files:

  • %Application Data%\Microsoft\Crypto\DSS\S-1-5-18\{random numbers}
  • %System%\Nwsapagent.dll

(Note: %Application Data% is the current user's Application Data folder, which is usually C:\Windows\Profiles\{user name}\Application Data on Windows 98 and ME, C:\WINNT\Profiles\{user name}\Application Data on Windows NT, and C:\Documents and Settings\{user name}\Local Settings\Application Data on Windows 2000, XP, and Server 2003.. %System% is the Windows system folder, which is usually C:\Windows\System on Windows 98 and ME, C:\WINNT\System32 on Windows NT and 2000, or C:\Windows\System32 on Windows XP and Server 2003.)

It creates the following folders:

  • %Application Data%\Microsoft\Crypto\DSS\S-1-5-18

(Note: %Application Data% is the current user's Application Data folder, which is usually C:\Windows\Profiles\{user name}\Application Data on Windows 98 and ME, C:\WINNT\Profiles\{user name}\Application Data on Windows NT, and C:\Documents and Settings\{user name}\Local Settings\Application Data on Windows 2000, XP, and Server 2003.)

Other System Modifications

This backdoor creates the following service using its DLL component:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\Nwsapagent

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\Nwsapagent
Type = "dword:00000110"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\Nwsapagent
Start = "2"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\Nwsapagent
ErrorControl = "1"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\Nwsapagent
ImagePath = "%SystemRoot%\System32\svchost.exe -k netsvcs"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\Nwsapagent
DisplayName = "Gateway Service for Netware"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\Nwsapagent
ObjectName = "LocalSystem"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\Nwsapagent\Parameters
ServiceDll = "%System%\Nwsapagent.dll"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\Nwsapagent
ObjectName = "LocalSystem"

NOTES:
It attempts to connect to the following IP address:

  • {BLOCKED}.{BLOCKED}.132.8

  SOLUTION

Minimum Scan Engine: 9.200

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, and then 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.



HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\
Nwsapagent

Step 3

Search and delete these files

[ Learn More ]
There may be some component 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.
  • %Application Data%\Microsoft\Crypto\DSS\S-1-5-18\{random numbers}
  • %System%\Nwsapagent.dll

Step 4

Search and delete this folder

[ Learn More ]
Please make sure you check the Search Hidden Files and Folders checkbox in the More advanced options option to include all hidden folders in the search result.
  • %Application Data%\Microsoft\Crypto\DSS\S-1-5-18

Step 5

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