Analysis by: Christopher Daniel So
ALIASES:

Backdoor:OSX/Imuler.A (FSecure)

 PLATFORM:

Mac OS X

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

  • Threat Type: Backdoor

  • Destructiveness: No

  • Encrypted: No

  • In the wild: Yes

  OVERVIEW

Infection Channel: Dropped by other malware

This backdoor may be dropped by other malware.

It runs certain commands that it receives remotely from a malicious user. Doing this puts the affected computer and information found on the computer at greater risk.

  TECHNICAL DETAILS

File Size: 104,712 bytes
File Type: Mach-O
Memory Resident: Yes
Initial Samples Received Date: 21 Mar 2012
Payload: Connects to URLs/IPs

Arrival Details

This backdoor may be dropped by the following malware:

  • OSX_IMULER.B

Installation

This backdoor drops the following copies of itself into the affected system:

  • /Users/{user name}/Library/LaunchAgents/checkvir

Autostart Technique

This backdoor drops the following files:

  • /Users/{user name}/Library/LaunchAgents/checkvir.plist

Backdoor Routine

This backdoor executes the following command(s) from a remote malicious user:

  • Take a screen shot
  • Update the C&C server name
  • List the contents of a folder and save it as /tmp/launch-0rp.dat. Then upload the file /tmp/launch-0rp.dat.
  • Get the file size of a file
  • Download a file from a URL
  • Execute a command via the shell
  • Delete a file
  • Download a file and save it as /tmp/xntaskz.gz. Decompress the downloaded file to /tmp/xntaskz. Execute the following command:
    /tmp/CurlUpload -f /tmp/xntaskz

It connects to the following URL(s) to send and receive commands from a remote malicious user:

  • http://www.{BLOCKED}sbutters.com/cgi-mac/

Download Routine

This backdoor accesses the following websites to download files:

  • http://www.{BLOCKED}sbutters.com/CurlUpload

It saves the files it downloads using the following names:

  • /tmp/CurlUpload

  SOLUTION

Minimum Scan Engine: 9.200
FIRST VSAPI PATTERN FILE: 8.866.05
FIRST VSAPI PATTERN DATE: 27 Mar 2012
VSAPI OPR PATTERN File: 8.867.00
VSAPI OPR PATTERN Date: 27 Mar 2012

Step 1

Remove the malware/grayware file that dropped/downloaded OSX_IMULER.C

NOTES:

Step 2

Delete the autostart file used by this malware. To delete the autostart file, open a Terminal window and type the following command:

rm "/Users/{user name}/Library/LaunchAgents/checkvir.plist"

Step 3

Terminate the malware process. To terminate the malware process, open a Terminal window and perform the following:

  1. Enter the following command:

    ps -A

  2. In the Terminal window, search for a line similar to the following:

    {number} ?? Ss {time} /Users/{user name}/Library/LaunchAgents/checkvir

    Take note of the number. This number is the malware process ID (PID)
  3. Enter the following command:

    kill {malware PID}

Step 4

Deleting the dropped files. To delete the dropped files, open a Terminal window and type the following commands:

rm /tmp/CurlUpload

rm /tmp/xntaskz

rm /tmp/xntaskz.gz

rm /tmp/launch-0rp.dat

Step 5

Scan your computer with your Trend Micro product to delete files detected as OSX_IMULER.C 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.

To open a Terminal window, double-click Applications > Utilities > Terminal in Finder.

To close the Terminal application, press ⌘ (Command) + Q.


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