Analysis by: Anthony Joe Melgarejo
ALIASES:

Trojan:Win32/Medfos.X (Microsoft), Trojan.Win32.Medfos.o (v) (Sunbelt), Win32/Medfos.LN trojan (ESET)

 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: Yes

  • In the wild: Yes

  OVERVIEW

This Trojan arrives as a component bundled with malware/grayware packages.

However, as of this writing, the said sites are inaccessible.

  TECHNICAL DETAILS

File Size: 334,336 bytes
File Type: DLL
Memory Resident: Yes
Initial Samples Received Date: 15 Mar 2013
Payload: Connects to URLs/IPs, Downloads files

Arrival Details

This Trojan arrives as a component bundled with malware/grayware packages.

Installation

This Trojan adds the following mutexes to ensure that only one of its copies runs at any one time:

  • {22222222-2222-2222-2222-222222222222}

Autostart Technique

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

HKEY_LOCAL_MACHINE\Software\Microsoft\
Windows\CurrentVersion\Run
{malware file name} = "rundll32.exe {malware path and file name}.dll,Check"

Information Theft

This Trojan accesses the following site to download its configuration file:

  • {BLOCKED}treport.com/wpad.dat

Other Details

However, as of this writing, the said sites are inaccessible.

NOTES:

Its configuration file allows the attacker to intercept and modify the affected systems' Internet traffic.

  SOLUTION

Minimum Scan Engine: 9.300
FIRST VSAPI PATTERN FILE: 9.790.02
FIRST VSAPI PATTERN DATE: 15 Mar 2013
VSAPI OPR PATTERN File: 9.791.00
VSAPI OPR PATTERN Date: 15 Mar 2013

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 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_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run
    • {malware file name} = "rundll32.exe {malware path and file name}.dll,Check"

Step 4

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