Analysis by: Roland Marco Dela Paz

ALIASES:

W32/Medfos.AD!tr (Fortinet); Medfos.e (McAfee)

 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

Infection Channel: Dropped by other malware

This Trojan modifies a certain file where it inserts a line line under the [ExtensionDirs] section.

This Trojan may be dropped by other malware.

As of this writing, the said sites are inaccessible.

  TECHNICAL DETAILS

File Size: Varies
File Type: DLL
Memory Resident: Yes
Initial Samples Received Date: 21 Jun 2012
Payload: Downloads files, Connects to URLs/IPs

Arrival Details

This Trojan may be dropped by other malware.

Installation

This Trojan adds the following processes:

  • default browser process

It creates the following folders:

  • %Application Data%\{AF8106AD-BA42-11E1-8270-B8AC6F996F26}

(Note: %Application Data% is the current user's Application Data folder, which is usually C:\Windows\Profiles\{user name}\Application Data on Windows 98 and ME, C:\WINNT\Profiles\{user name}\Application Data on Windows NT, and C:\Documents and Settings\{user name}\Local Settings\Application Data on Windows 2000, XP, and Server 2003.)

Other System Modifications

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

HKEY_CURRENT_USER\Software\Mozilla\
Firefox\Extensions
{AF8106AD-BA42-11E1-8270-B8AC6F996F26} = %Application Data%\{AF8106AD-BA42-11E1-8270-B8AC6F996F26}

Download Routine

This Trojan accesses the following websites to download files:

  • http://{BLOCKED}oadfile.com/file/id=AwAyAAEAyq8QAAEFAJAAAAAAAAAAIwwGEAsAAACtBoGv4RFCuqy4cIImb5lvVVVVVVVVVVVVVVVVVVVVVQAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAADRW&c=3
  • http://{BLOCKED}load.com/file/id=BAAyAAEAvTwQAAEFBgAAAAAAAAAAAAAAAAAAAAAjDAYQCwAAAO shSLhEUC6rLhwgiZvmW8AAFVVVVVVVVVVVVVVVVVVVVVPTs0BuoP8V5PYPABURUtFV19WTn9XR08uTEtGMjYyAhORIicbl80HAAAAAAA0VgAA&rt=AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA

As of this writing, the said sites are inaccessible.

NOTES:

This Trojan modifies the file %User Profile%\Mozilla\Firefox\Profiles\4wwmjcqo.default\extensions.ini where it inserts the following line under the [ExtensionDirs] section:

  • %Application Data%\{AF8106AD-BA42-11E1-8270-B8AC6F996F26}

  SOLUTION

Minimum Scan Engine: 9.200
FIRST VSAPI PATTERN FILE: 9.210.03
FIRST VSAPI PATTERN DATE: 22 Jun 2012

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

Restart in Safe Mode

[ Learn More ]

Step 3

Search and delete these folders

[ Learn More ]
Please make sure you check the Search Hidden Files and Folders checkbox in the More advanced options option to include all hidden folders in the search result.
  • %Application Data%\{AF8106AD-BA42-11E1-8270-B8AC6F996F26}

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\Mozilla\Firefox\Extensions
    • {AF8106AD-BA42-11E1-8270-B8AC6F996F26} = %Application Data%\{AF8106AD-BA42-11E1-8270-B8AC6F996F26}

Step 5

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

Step 6

Restore this file from backup only Microsoft-related files will be restored. If this malware/grayware also deleted files related to programs that are not from Microsoft, please reinstall those programs on you computer again.

  • %User Profile%\Mozilla\Firefox\Profiles\4wwmjcqo.default\extensions.ini


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