Analysis by: Abraham Latimer Camba
ALIASES:

Mal/Medfos-M, Mal/Medfos-M (Sophos), a variant of Win32/Medfos.JK trojan (ESET), Medfos-FAVB!2E97176E4A5C (McAfee), Trojan.Win32.Medfos.o (v) (Sunbelt)

 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:

  • 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.

It modifies files, disabling programs and applications from properly running.

  TECHNICAL DETAILS

File Size: Varies
File Type: DLL
Initial Samples Received Date: 02 Feb 2013

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.

Installation

This Trojan adds the following folders:

  • %User Profile%\Application Data\Mozilla\Firefox\Profiles\4wwmjcqo.default\extensions\{random CLSID}
  • %User Profile%\Application Data\Mozilla\Firefox\Profiles\4wwmjcqo.default\extensions\{random CLSID}\chrome
  • %User Profile%\Application Data\Mozilla\Firefox\Profiles\4wwmjcqo.default\extensions\{random CLSID}\chrome\content

(Note: %User Profile% is the current user's profile folder, which is usually C:\Documents and Settings\{user name} on Windows 2000, XP, and Server 2003, or C:\Users\{user name} on Windows Vista and 7.)

It drops the following files:

  • %Application Data%\{random CLSID}.crx
  • %Application Data%\Google\Chrome\Application\{chrome version}\Extensions\{random CLSID}.crx
  • %Application Data%\Google\Chrome\Application\{chrome version}\Extensions\{random string 1}.json
  • %User Profile%\Application Data\Mozilla\Firefox\Profiles\4wwmjcqo.default\extensions.sqlite
  • %User Profile%\Application Data\Mozilla\Firefox\Profiles\4wwmjcqo.default\extensions\{random CLSID}\chrome.manifest
  • %User Profile%\Application Data\Mozilla\Firefox\Profiles\4wwmjcqo.default\extensions\{random CLSID}\chrome\content\browser.xul
  • %User Profile%\Application Data\Mozilla\Firefox\Profiles\4wwmjcqo.default\extensions\{random CLSID}\install.rdf

(Note: %Application Data% is the current user's Application Data folder, which is usually C:\Documents and Settings\{user name}\Application Data on Windows 2000, XP, and Server 2003, or C:\Users\{user name}\AppData\Roaming on Windows Vista and 7.. %User Profile% is the current user's profile folder, which is usually C:\Documents and Settings\{user name} on Windows 2000, XP, and Server 2003, or C:\Users\{user name} on Windows Vista and 7.)

Other System Modifications

This Trojan modifies the following files:

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

(Note: %User Profile% is the current user's profile folder, which is usually C:\Documents and Settings\{user name} on Windows 2000, XP, and Server 2003, or C:\Users\{user name} on Windows Vista and 7.)

It adds the following registry keys:

HKEY_LOCAL_MACHINE\SOFTWARE\Google\
Chrome

HKEY_LOCAL_MACHINE\SOFTWARE\Google\
Chrome\Extensions

HKEY_LOCAL_MACHINE\SOFTWARE\Google\
Chrome\Extensions\{random string 1}

It adds the following registry entries:

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion
rcprn = "{random string 2}"

HKEY_LOCAL_MACHINE\SOFTWARE\Google\
Chrome\Extensions\{random string 1}
path = "%Application Data%\{random CLSID}.crx"

HKEY_LOCAL_MACHINE\SOFTWARE\Google\
Chrome\Extensions\{random string 1}
version = "1"

Other Details

This Trojan connects to the following possibly malicious URL:

  • http://{BLOCKED}load.com/upload/fid={random value}