Analysis by: RonJay Kristoffer Caragay

ALIASES:

Trojan:Win32/Rimod!gmb (Microsoft); W32/AutoRun-BTU (Sophos); Worm.AutoRun (VBA32); Worm.Win32.AutoRun.dkcq (Kaspersky); Win32/AutoRun.VB.ARV (ESET-NOD32);

 PLATFORM:

Windows

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

  • Threat Type: Worm

  • Destructiveness: No

  • Encrypted: No

  • In the wild: Yes

  OVERVIEW

Infection Channel: Propagates via removable drives, Downloaded from the Internet, Dropped by other malware

This worm arrives via removable drives. It arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.

It creates folders in all physical and removable drives. It drops an AUTORUN.INF file to automatically execute the copies it drops when a user accesses the drives of an affected system.

It does not have any backdoor routine.

  TECHNICAL DETAILS

File Size: 270,336 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 29 Sep 2015
Payload: Terminates processes

Arrival Details

This worm arrives via removable drives.

It 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 worm drops the following copies of itself into the affected system:

  • %Program Files%\SKM_AD\SKM_AD1.exe
  • {Drive Letter}:\SKM_AD\SKM_AD1.exe

(Note: %Program Files% is the Program Files folder, where it usually is C:\Program Files on all Windows operating system versions; C:\Program Files (x86) for 32-bit applications running on Windows 64-bit operating systems.)

It creates the following folders:

  • %Program Files%\SKM_AD
  • {Drive Letter}:\SKM_AD

(Note: %Program Files% is the Program Files folder, where it usually is C:\Program Files on all Windows operating system versions; C:\Program Files (x86) for 32-bit applications running on Windows 64-bit operating systems.)

Autostart Technique

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

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Run
SKM_AD = "%Program Files%\SKM_AD\SKM_AD1.exe"

Other System Modifications

This worm modifies the following registry entries:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Explorer\
Advanced\Folder\SuperHidden
CheckedValue = "{random value}"

(Note: The default value data of the said registry entry is 0.)

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Explorer\
Advanced\Folder\SuperHidden
UncheckedValue = "{random value}"

(Note: The default value data of the said registry entry is 1.)

Propagation

This worm creates the following folders in all physical and removable drives:

  • {Drive Letter}:\SKM_AD

It drops the following copies of itself in all physical and removable drives:

  • {Drive Letter}:\SKM_AD\SKM_AD1.exe

It drops an AUTORUN.INF file to automatically execute the copies it drops when a user accesses the drives of an affected system.

The said .INF file contains the following strings:

[autorun]
shellexecute=SKM_AD\skm_ad1.exe
icon=%SystemRoot%\system32\SHELL32.dll,7
action=Scan drive for viruses
shell\1=Open
shell\1\command=SKM_AD\skm_ad1.exe
shell\2=Explore
shell\2\command=SKM_AD\skm_ad1.exe
shell\3=Search
shell\3\command=SKM_AD\skm_ad1.exe

Backdoor Routine

This worm does not have any backdoor routine.

Process Termination

This worm terminates the following processes if found running in the affected system's memory:

  • skm_ad.exe

NOTES:

It searches for the following files:

  • %Program Files%\SKM_AD\new.txt
  • C:\19811221.luv

  SOLUTION

Minimum Scan Engine: 9.750
FIRST VSAPI PATTERN FILE: 11.950.03
FIRST VSAPI PATTERN DATE: 30 Sep 2015
VSAPI OPR PATTERN File: 11.951.00
VSAPI OPR PATTERN Date: 01 Oct 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_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
    • SKM_AD = "%Program Files%\SKM_AD\SKM_AD1.exe"

Step 5

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.
  • %Program Files%\SKM_AD
  • {Drive Letter}:\SKM_AD

Step 6

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.
  • %Program Files%\SKM_AD\new.txt
  • C:\19811221.luv

Step 7

Search and delete AUTORUN.INF files created by WORM_RIMOD.AV that contain these strings

[ Learn More ]
[autorun]
shellexecute=SKM_AD\skm_ad1.exe
icon=%SystemRoot%\system32\SHELL32.dll,7
action=Scan drive for viruses
shell\1=Open
shell\1\command=SKM_AD\skm_ad1.exe
shell\2=Explore
shell\2\command=SKM_AD\skm_ad1.exe
shell\3=Search
shell\3\command=SKM_AD\skm_ad1.exe

Step 8

Restore this modified 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_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\Advanced\Folder\SuperHidden
    • From: CheckedValue = "{random value}"
      To: CheckedValue = 0
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\Advanced\Folder\SuperHidden
    • From: UncheckedValue = "{random value}"
      To: UncheckedValue = 1

Step 9

Restart in normal mode and scan your computer with your Trend Micro product for files detected as WORM_RIMOD.AV. 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 10

Scan your computer with your Trend Micro product to delete files detected as WORM_RIMOD.AV. 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.


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