Analysis by: Rhena Inocencio
ALIASES:

Trojan:Win32/Medfos.gen!E (Microsoft), Medfos-FAK!637F75F6E47C (McAfee), a variant of Win32/Medfos.YC (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:
 INFORMATION EXPOSURE:

  • Threat Type: Trojan

  • Destructiveness: No

  • Encrypted: Yes

  • In the wild: Yes

  OVERVIEW

This Trojan may arrive bundled with malware packages as a malware component. It 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: Varies
File Type: DLL
Memory Resident: Yes
Initial Samples Received Date: 04 Dec 2013

Arrival Details

This Trojan may arrive bundled with malware packages as a malware component.

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

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 filename} = "rundll32 {malware path and filename},RuntimeError"

Other System Modifications

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

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion
{malware filename} = "{random values}"

Other Details

This Trojan connects to the following possibly malicious URL:

  • {BLOCKED}llppcsite.com

  SOLUTION

Minimum Scan Engine: 9.700
FIRST VSAPI PATTERN FILE: 10.454.01
FIRST VSAPI PATTERN DATE: 04 Dec 2013
VSAPI OPR PATTERN File: 10.455.00
VSAPI OPR PATTERN Date: 05 Dec 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

Scan your computer with your Trend Micro product and note files detected as TROJ_MEDFOS.SML

Step 3

Restart in Safe Mode

[ Learn More ]

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_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
    • {malware filename} = "rundll32 {malware path and filename},RuntimeError"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion
    • {malware filename} = "{random values}"

Step 5

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