Modified by: Sabrina Lei Sioting
ALIASES:

TrojanDownloader:Win32/Fosniw.B (Microsoft), Troj/Fosniw-F (Sophos), Trojan-Downloader.Win32.Fosniw.f.2 (Sunbelt), W32/Fosniw.B.gen!Eldorado (Authentium), W32/Fosniw.AP!tr (Fortinet), Trojan-Downloader.Fosniw (VBA32)

 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: Trojan

  • Destructiveness: No

  • Encrypted: No

  • In the wild: Yes

  OVERVIEW

Infection Channel: Downloaded from the Internet, Dropped by other malware

This Trojan arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.

As of this writing, the said sites are inaccessible.

  TECHNICAL DETAILS

File Size: 264,192 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 22 Dec 2011
Payload: Connects to URLs/IPs, Downloads files

Arrival Details

This Trojan 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 Trojan drops the following copies of itself into the affected system:

  • %Application Data%\rint.exe

(Note: %Application Data% is the current user's Application Data folder, which is usually C:\Documents and Settings\{user name}\Application Data on Windows 2000, XP, and Server 2003, or C:\Users\{user name}\AppData\Roaming on Windows Vista and 7.)

Autostart Technique

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

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
d2d0dbcdd6d1cb91dac7da = "%Application Data%\rint.exe"

Other System Modifications

This Trojan adds the following registry entries as part of its installation routine:

HKEY_CURRENT_USER\Software\bfb396eaa9cf
DC = "4"

HKEY_CURRENT_USER\Software\bfb396eaa9cf
idt = "{date and time}"

HKEY_CURRENT_USER\Software\bfb396eaa9cf
ver = "1.0.0.114"

HKEY_CURRENT_USER\Software\bfb396eaa9cf
Location = "d2d0dbcdd6d1cb91dac7da"

HKEY_CURRENT_USER\Software\bfb396eaa9cf
pid = "cln1"

HKEY_CURRENT_USER\Software\bfb396eaa9cf
prj = "2"

It adds the following registry keys as part of its installation routine:

HKEY_CURRENT_USER\Software\bfb396eaa9cf

Download Routine

This Trojan connects to the following website(s) to download and execute a malicious file:

  • http://{BLOCKED}reasys{number}.com/app.asp?prj=2&pid=cln1&logdata=MacTryCnt:0&code=&ver=1.0.0.114&appcheck=1
  • http://{BLOCKED}reasys{number}.com/setup_b.asp?prj=2&pid=cln1&mac=000c29551670
  • http://{BLOCKED}asys{number}.com/receive/r_autoidcnt.asp?mer_seq=2&realid=cln1&cnt_type=e2&mac=000c29551670&logdata=MacTryCnt:0

As of this writing, the said sites are inaccessible.

  SOLUTION

Minimum Scan Engine: 9.300
FIRST VSAPI PATTERN FILE: 8.660.09
FIRST VSAPI PATTERN DATE: 22 Dec 2011

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

Identify and terminate files detected as TROJ_FOSNIW.SMWP

[ Learn More ]
  1. Windows Task Manager may not display all running processes. In this case, please use a third-party process viewer, preferably Process Explorer, to terminate the malware/grayware/spyware file. You may download the said tool here.
  2. If the detected file is displayed in either Windows Task Manager or Process Explorer but you cannot delete it, restart your computer in safe mode. To do this, refer to this link for the complete steps.
  3. If the detected file is not displayed in either Windows Task Manager or Process Explorer, continue doing the next steps.

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. Before you could do this, you must restart in Safe Mode. For instructions on how to do this, you may refer to this page If the preceding step requires you to restart in safe mode, you may proceed to edit the system registry.

 
  • In HKEY_CURRENT_USER\Software
    • bfb396eaa9cf

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_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
    • d2d0dbcdd6d1cb91dac7da = "%Application Data%\rint.exe"

Step 5

Scan your computer with your Trend Micro product to delete files detected as TROJ_FOSNIW.SMWP. 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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