Analysis by: Michelle Morales
ALIASES:

Trojan:Win32/Kilim.gen!C (Microsoft);

 PLATFORM:

Windows

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

  • Threat Type: Trojan

  • Destructiveness: No

  • Encrypted: Yes

  • In the wild: Yes

  OVERVIEW

Infection Channel: Downloaded from the Internet

This Trojan may be unknowingly downloaded by a user while visiting malicious websites.

  TECHNICAL DETAILS

File Size: 677,059 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 02 Feb 2015
Payload: Steals information, Connects to URLs/IPs, Modifies HOSTS file

Arrival Details

This Trojan may be unknowingly downloaded by a user while visiting malicious websites.

Installation

This Trojan drops the following copies of itself into the affected system and executes them:

  • %Application Data%\Chromium.exe

(Note: %Application Data% is the Application Data folder, where it usually is C:\Documents and Settings\{user name}\Application Data on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\AppData\Roaming on Windows Vista (32- and 64-bit), Windows 7 (32- and 64-bit), Windows 8 (32- and 64-bit), Windows 8.1 (32- and 64-bit), Windows Server 2008, and Windows Server 2012.)

It drops and executes the following files:

  • %Application Data%\wget.exe <-- this file is used to download arsiv.exe and is deleted after download

(Note: %Application Data% is the Application Data folder, where it usually is C:\Documents and Settings\{user name}\Application Data on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\AppData\Roaming on Windows Vista (32- and 64-bit), Windows 7 (32- and 64-bit), Windows 8 (32- and 64-bit), Windows 8.1 (32- and 64-bit), Windows Server 2008, and Windows Server 2012.)

Autostart Technique

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

HKEY_CURRENT_USER\SOFTWARE\Microsoft\
Windows\CurrentVersion\Run
Google Chromium = "%Application Data%\Chromium.exe"

Other System Modifications

This Trojan adds the following registry entries:

HKEY_LOCAL_MACHINE\SOFTWARE\Policies\
Google\Update
UpdateDefault = "0" <-- this registry entry disables automatic google update

It also creates the following registry entry(ies) as part of its installation routine:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\policies\
System
EnableLUA = "0" <-- this registry entry disables user notification when programs try to install software or make changes to the computer

Download Routine

This Trojan connects to the following URL(s) to download its component file(s):

  • http://www.{BLOCKED}r.com/ahk/req.php?type=arsiv_link
  • http://{BLOCKED}r.com/ahk/ok.txt
  • http://{BLOCKED}r.com/ahk/req.php?type=update_hash
  • http://{BLOCKED}r.com/ahk/req.php?type=js
  • http://filmver.com/ahk/req.php?type=key
  • http://filmver.com/ahk/req.php?type=arsiv_hash

It saves the files it downloads using the following names:

  • %Application Data%\arsiv.exe <-- this file is the installer of the Chrome version the malware needs to install
  • %Application Data%\update.txt
  • %Application Data%\bg.txt <-- this file contains script for chrome browser extension
  • %Application Data%\hash.txt <-- this file contains the hash of the original executable file of chrome
  • %Application Data%\ok.txt <-- this file indicates if server it connects to is still up

(Note: %Application Data% is the Application Data folder, where it usually is C:\Documents and Settings\{user name}\Application Data on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\AppData\Roaming on Windows Vista (32- and 64-bit), Windows 7 (32- and 64-bit), Windows 8 (32- and 64-bit), Windows 8.1 (32- and 64-bit), Windows Server 2008, and Windows Server 2012.)

HOSTS File Modification

This Trojan overwrites the system's HOSTS files to prevent users from accessing the following websites:

  • tools.google.com
  • clients4.google.com

Other Details

This Trojan connects to the following URL(s) to check for an Internet connection:

  • http://www.google.com

NOTES:

This Trojan replaces the current version of Google Chrome installed in the system into an older version.

It drops the following Google Chrome extension files:

  • %AppDataLocal%\Google\Chrome\User Data\Default\Extensions\{long string from key.txt}\bg.txt -->this is a copy of the downloaded bg.txt file
  • %AppDataLocal%\Google\Chrome\User Data\Default\Preferences --> this file is a configuration file for bg.txt

It also checks for the following browsers:

  • Mozilla Firefox
  • Opera Launcher

If the said browsers are present, the malware drops {browser}.exe, detected as TROJ_KILIM.EFKY, under the original browser folder. The dropped file uses the file icon of Google Chrome and when executed opens the installed version of Google Chrome instead of the preferred browser.

It is also capable of phishing for the user's Google account information. Upon the first execution of the browser, the browser loads the Google account sign in page prompting the user to log in to their account.

  SOLUTION

Minimum Scan Engine: 9.700
FIRST VSAPI PATTERN FILE: 11.456.05
FIRST VSAPI PATTERN DATE: 02 Feb 2015
VSAPI OPR PATTERN File: 11.457.00
VSAPI OPR PATTERN Date: 03 Feb 2015

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

Note that not all files, folders, and registry keys and entries are installed on your computer during this malware's/spyware's/grayware's execution. This may be due to incomplete installation or other operating system conditions. If you do not find the same files/folders/registry information, please proceed to the next step.

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_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
    • Google Chromium = "%Application Data%\Chromium.exe"

Step 5

Delete this registry key

[ 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.

  • HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Google\Update

Step 6

Remove these strings added by the malware/grayware/spyware in the HOSTS file

[ Learn More ]
    • 127.0.0.1 tools.google.com
    • 127.0.0.1 clients4.google.com

Step 7

Search and delete this file

[ Learn More ]
There may be some 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.
  • %Application Data%\arsiv.exe
  • %Application Data%\ok.txt
  • %Application Data%\bg.txt
  • %Application Data%\update.txt
  • %Application Data%\hash.txt
  • %Application Data%\key.txt

Step 8

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

NOTES:
Re-install browsers to latest version.


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