Threat Encyclopedia

OSX_DNSCHAN.A

Malware type: Trojan

Aliases: OSX/RSPlug-Gen (Sophos),

In the wild: Yes

Destructive: No

Language: English

Platform: Mac OS X

Encrypted: No

Overall risk rating:

Reported infections:

Damage potential:

Medium

Distribution potential:

Low

Description: 

To get a one-glance comprehensive view of the behavior of this malware, refer to the Behavior Diagram shown below.

OSX_DNSCHAN.A Behavior Diagram

Malware Overview

This Trojan arrives as a DMG file downloaded from a certain Web site. A DMG file is a mountable disk image created in Mac OS X, and is commonly used for software installers downloaded from the Internet.

It tricks the user into thinking that a legitimate video codec program is being installed. It even includes an End User License Agreement (EULA) to complete its scam. However, once running on an affected system, this Trojan drops a malicious Bash script files detected by Trend Micro as UNIX_DNSCHAN.A. As a result, routines of the dropped malware are also exhibited on the system.

Two versions of this malware exists, depending on the Internet browser and operating system used to download it (Windows or Mac OS X). Note that one of the two versions can be downloaded on the same remote site.

For additional information about this threat, see:

Description created: Nov. 1, 2007 5:34:11 AM GMT -0800


TECHNICAL DETAILS


File type: DMG

Memory resident:  No

Size of malware: Varies

Initial samples received on: Nov 1, 2007

Related toUNIX_DNSCHAN.A

Payload 1: Drops files

Details:

Arrival and Installation

This Trojan can be downloaded from the following remote site:

  • http://{BLOCKED}odec.com/download/ultracodec{number}.dmg

It arrives on the affected system as a DMG file. A DMG file is a mountable disk image created in Mac OS X, and is commonly used for software installers downloaded from the Internet.

This Trojan tricks the user into thinking that a legitimate video codec program is being installed. It also includes an End User License Agreement (EULA).

Dropping Routine

Upon the completion of its installation routine, this Trojan drops the malicious Bash script file detected by Trend Micro as UNIX_DNSCHAN.A.

Other Details

Two versions of this malware exists, depending on the Internet browser and operating system used to download it (Windows or Mac OS X). Note that one of the two versions can be downloaded on the same remote site.

When using a Windows platform to connect to the malicious Web site, the downloaded file also uses a .DMG extension. However, examining its contents would show that it is actually an EXE file.

Affected Platforms

This Trojan runs on Mac OS X.

Analysis By: John Symelle Ortiz Luis

Revision History:

First pattern file version: 4.808.09
First pattern file release date: Nov 01, 2007

SOLUTION


Minimum scan engine version needed: 8.300

Pattern file needed: 4.894.14

Pattern release date: Dec 18, 2007


Important note: The "Minimum scan engine" refers to the earliest Trend Micro scan engine version guaranteed to detect this threat. However, Trend Micro strongly recommends that you update to the latest version in order to get comprehensive protection. Download the latest scan engine here.

Solution:

Note: To fully remove all associated malware, perform the clean solution for UNIX_DNSCHAN.A.

Running Trend Micro Antivirus

Although this malware primarily targets Mac computers, its spread mechanism may allow it to enter Microsoft (MS) Windows computers as well. To rid your MS Windows PC of this malware, run your Trend Micro antivirus product.

If you are currently running in safe mode, please restart your computer normally before performing the following solution.

Scan your computer with Trend Micro antivirus and delete files detected as OSX_DNSCHAN.A. To do this, Trend Micro customers must download the latest virus pattern file and scan their computers. Other Internet users can use HouseCall, the Trend Micro online threat scanner.




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