Analysis by: Michael Cabel
 PLATFORM:

Windows 2000, XP, 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 dropped by other malware.

  TECHNICAL DETAILS

File Size: 6,656 bytes
File Type: DLL
Memory Resident: Yes
Initial Samples Received Date: 20 Sep 2010
Payload: Connects to URLs/Ips

Arrival Details

This backdoor may be dropped by the following malware:

  • TROJ_DROPPR.KEN

Installation

This backdoor is injected into the following processes running in memory:

  • svchost.exe

Autostart Technique

This backdoor registers itself as a system service to ensure its automatic execution at every system startup by adding the following registry entries:

HKEY_LOCAL_MACHINE
Type = dword:00000020

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\Irmon
Start = dword:00000002

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\Irmon
ErrorControl = dword:00000001

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\Irmon
ImagePath = hex(2):%SystemRoot%\System32\svchost.exe -k netsvcs

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

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\Irmon\Parameters
ServiceDll = hex(2):C:\WINDOWS\system32\ahnsy.dll

Other Details

This backdoor connects to the following possibly malicious URL:

  • {BLOCKED}03.myfw.us

It does the following:

  • Arrives as a dropped file of TROJ_DROPPR.KEN and is typically saved as %System%\ahnsy.dll

(Note: %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.)

  SOLUTION

Minimum Scan Engine: 8.900
FIRST VSAPI PATTERN FILE: 7.478.02
FIRST VSAPI PATTERN DATE: 20 Sep 2010
VSAPI OPR PATTERN File: 7.479.00
VSAPI OPR PATTERN Date: 21 Sep 2010

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

Remove malware files dropped/downloaded by BKDR_AHNSY.B

    TROJ_DROPPR.KEN

Step 3

Restart in Safe Mode

[ Learn More ]

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.

Step 5

Search and delete this file

[ 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. %System%\ahnsy.dll

Step 6

Scan your computer with your Trend Micro product to delete files detected as BKDR_AHNSY.B. 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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