Analysis by: Karl Dominguez
ALIASES:

Microsoft: TrojanDownloader:Win32/Renos.PT ; Sophos : Mal/FakeAV-IZ

 PLATFORM:

Windows 2000, Windows XP, Windows Server 2003

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

  • Threat Type: Trojan

  • Destructiveness: No

  • Encrypted: Yes

  • In the wild: Yes

  OVERVIEW

This Trojan injects itself into certain web browsers to monitor searches made by the user in http://google.com.

It connects to certain URLs to send the gathered information which may be used by the remote user for blackhat search engine optimization (SEO). These URLs are also known to host FAKEAV malware.

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

  TECHNICAL DETAILS

File Size: Varies
File Type: PE
Memory Resident: Yes
Initial Samples Received Date: 01 Jun 2011
Payload: Connects to URLs/IPs

Arrival Details

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

Installation

This Trojan drops the following files:

  • %System%\sshnas21.dll - also detected as TROJ_RENOS.SM10

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

It injects itself into the following processes as part of its memory residency routine:

  • svchost.exe

Autostart Technique

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

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\SSHNAS
Type = "20"

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

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\SSHNAS
ErrorControl = "0"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\SSHNAS
ImagePath = "%System%\svchost.exe -k netsvcs"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\SSHNAS
DisplayName = "SSHNAS"

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

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\SSHNAS\Parameters
ServiceDll = "%System%\sshnas21.dll"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\SSHNAS\Security
Security = "{hex values}"

It modifies the following registry entry(ies) to enable its automatic execution at every system startup:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\SvcHost
netsvcs = {default services} SSHNAS

(Note: The default value data of the said registry entry is {default services}.)

Other System Modifications

This Trojan adds the following registry keys:

HKEY_CURRENT_USER\Software\Microsoft\
idgbn5xehg

It adds the following registry entries:

HKEY_CURRENT_USER\Software\Microsoft\
idgbn5xehg
wd29 = "{hex values}"

NOTES:

It injects itself into the following web browsers to monitor searches made by the user in http://google.com:

  • mozilla.exe
  • iexplore.exe
  • opera.exe
  • firefox.exe
  • safari.exe
  • maxthon.exe

It connects to the following URLs to send the gathered information which may be used by the remote user for blackhat search engine optimization (SEO). These URLs are also known to host FAKEAV malware:

  • http://{BLOCKED}ng.com/tbd.php
  • http://{BLOCKED}ty.com/tbd.php
  • http://{BLOCKED}life.com/tbd.php
  • http://{BLOCKED}tl.com/oms.php
  • http://{BLOCKED}del.com/oms.php

  SOLUTION

Minimum Scan Engine: 8.900
FIRST VSAPI PATTERN FILE: 8.194.08
FIRST VSAPI PATTERN DATE: 01 Jun 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

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_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services
    • SSHNAS
  • In HKEY_CURRENT_USER\Software\Microsoft
    • idgbn5xehg

Step 4

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\SvcHost
    • From: netsvcs = {default services} SSHNAS
      To: netsvcs = {default services}

Step 5

Restart in normal mode and scan your computer with your Trend Micro product for files detected as TROJ_RENOS.SM10. 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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