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TROJ_MIRSA.B

October 13, 2012
 ALIASES:

TrojanDropper:Win32/Small.SB (Microsoft); [000085e0.EXE\000085e0.EXE]:Downloader-VV, [000061e0.EXE\000061e0.EXE]:Spyre.dll (McAfee); Downloader (Symantec); Trojan-Dropper.Win32.Small.oy (Kaspersky); Trojan.Win32.Generic!BT (Sunbelt); Trojan.Downloader.AA (FSecure)

 PLATFORM:

Windows 2000, Windows XP, Windows Server 2003

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

  • Threat Type: Trojan

  • Destructiveness: No

  • Encrypted:

  • In the wild: Yes

  OVERVIEW


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.

  TECHNICAL DETAILS

File Size:

53,248 bytes

File Type:

EXE

Memory Resident:

No

Initial Samples Received Date:

18 May 2012

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.

Other System Modifications

This Trojan modifies the following registry entries:

HKEY_CURRENT_USER\SessionInformation
ProgramCount = "1"

(Note: The default value data of the said registry entry is 2.)

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
DirectDraw\MostRecentApplication
Name = "iexplore.exe"

(Note: The default value data of the said registry entry is iexplore.exe.)

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
DirectDraw\MostRecentApplication
ID = "4117b81"

(Note: The default value data of the said registry entry is 41107b81.)

Dropping Routine

This Trojan drops the following files:

  • %System%\srpcsrv32.dll
  • %System%\spoolsrv32.exe
  • %Windows%\Web\desktop.html
  • %System%\txfdb32.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.. %Windows% is the Windows folder, which is usually C:\Windows or C:\WINNT.)

Other Details

This Trojan connects to the following possibly malicious URL:

  • http://{BLOCKED}ch.cc/n.php?242
  • http://{BLOCKED}177.100/st.php?242&e=2

This report is generated via an automated analysis system.

  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

Restore this modified 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\SessionInformation
    • From: ProgramCount = "1"
      To: ProgramCount = ""2""
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\DirectDraw\MostRecentApplication
    • From: Name = "iexplore.exe"
      To: Name = ""iexplore.exe""
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\DirectDraw\MostRecentApplication
    • From: ID = "4117b81"
      To: ID = ""41107b81""

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.
  • %System%\srpcsrv32.dll
  • %System%\spoolsrv32.exe
  • %Windows%\Web\desktop.html
  • %System%\txfdb32.dll

Step 4

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