Threat Encyclopedia

BKDR_ANDROM.AS

Publish date: February 05, 2013

ANALYSIS BY

Mark Joseph Manahan


ALIASES:

Win32/TrojanDownloader.Wauchos.A (Eset), Worm:Win32/Gamarue.I (Microsoft)

PLATFORM:

Windows 2000, Windows XP, Windows Server 2003

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

  • Threat Type:Backdoor

  • Destructiveness:No

  • Encrypted: Yes

  • In the wild: Yes

OVERVIEW

Infection Channel:

Spammed via email


This backdoor arrives as an attachment to email messages spammed by other malware/grayware or malicious users.

It executes commands from a remote malicious user, effectively compromising the affected system.

TECHNICAL DETAILS

File Size:

63,847 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

17 Oct 2012

Payload:

Compromises system security, Connects to URLs/IPs, Downloads files

Arrival Details

This backdoor arrives as an attachment to email messages spammed by other malware/grayware or malicious users.

Installation

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

  • %System Root%\Documents and Settings\All Users\svchost.exe
  • %System Root%\Documents and Settings\All Users\Local Settings\Temp\ms{random characters}.{extension name}

(Note: %System Root% is the root folder, which is usually C:\. It is also where the operating system is located.)

It adds the following mutexes to ensure that only one of its copies runs at any one time:

  • {Decimal form of the Volume Serial Number of %System Root%}

(Note: %System Root% is the root folder, which is usually C:\. It is also where the operating system is located.)

It stays memory-resident by injecting codes into the following processes:

  • \system32\wuauclt.exe
  • \syswow64\svchost.exe

Autostart Technique

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

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Run
SunJavaUpdateSched = "%System Root%\Documents and Settings\All Users\svchost.exe"

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\policies\
Explorer\Run
{random number} = "%System Root%\Documents and Settings\All Users\Local Settings\Temp\ms{random characters}.{extension name}"

Other System Modifications

This backdoor creates the following registry entry(ies) to bypass Windows Firewall:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\SharedAccess\Parameters\
FirewallPolicy\StandardProfile\AuthorizedApplications\
List
{malware path}\{malware name}.exe = "{malware path}\{malware name}.exe:*:Enabled:{malware name}"

Backdoor Routine

This backdoor executes the following commands from a remote malicious user:

  • Download a file from C&C server and save it as %User Temp%\{random number}.exe
  • Download a file from C&C server and save it in the folder %System Root%\Documents and Settings\All Users\ms{random number}.dat and loads it
  • Start a process
  • Uninstall itself
  • Remote command prompt

(Note: %User Temp% is the current user's Temp folder, which is usually C:\Documents and Settings\{user name}\Local Settings\Temp on Windows 2000, XP, and Server 2003, or C:\Users\{user name}\AppData\Local\Temp on Windows Vista and 7.. %System Root% is the root folder, which is usually C:\. It is also where the operating system is located.)

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

  • http://{BLOCKED}ecost.com/ff/image.php
  • http://{BLOCKED}agdpp43gn56.com/ff/image.php
  • http://{BLOCKED}uianowj12.com/ff/image.php
  • http://{BLOCKED}329sbgn56.com/ff/image.php

Other Details

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

  • www.update.microsoft.com

NOTES:

The {extension name} of the dropped copy is any of the following:

  • bat
  • cmd
  • com
  • exe
  • pif
  • scr

SOLUTION

Minimum Scan Engine:

9.200

FIRST VSAPI PATTERN FILE:

9.466.04

FIRST VSAPI PATTERN DATE:

17 Oct 2012

VSAPI OPR PATTERN File:

9.467.00

VSAPI OPR PATTERN Date:

18 Oct 2012

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

Scan your computer with your Trend Micro product and note files detected as BKDR_ANDROM.AS

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
    • SunJavaUpdateSched = "%System Root%\Documents and Settings\All Users\svchost.exe"

Step 5

Delete the registry entry with an unknown data 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\policies\Explorer\Run
    • {random number} = "%System Root%\Documents and Settings\All Users\Local Settings\Temp\ms{random characters}.{extension name}"
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\SharedAccess\Parameters\FirewallPolicy\StandardProfile\AuthorizedApplications\List
    • {malware path}\{malware name}.exe = "{malware path}\{malware name}.exe:*:Enabled:{malware name}"

Step 6

Search and delete these files

[ Learn More ]
There may be some component 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.
%User Temp%\{random number}.exe
%System Root%\Documents and Settings\All Users\ms{random number}.dat

Step 7

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