Analysis by: Emilio Marcel Garcia
ALIASES:

Trojan:Win32/CryptInject!MSR (MICROSOFT); HEUR:Trojan.Java.Agent.gen (KASPERSKY)

 PLATFORM:

Windows

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

  • Threat Type: Backdoor

  • Destructiveness: No

  • Encrypted:

  • In the wild: Yes

  OVERVIEW

This Backdoor arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.

However, as of this writing, the said sites are inaccessible.

  TECHNICAL DETAILS

File Size: 471,980 bytes
File Type: JAR
Initial Samples Received Date: 03 Feb 2020

Arrival Details

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

  • %User Profile%\bSBAJ\rAbvl.class

(Note: %User Profile% is the current user's profile folder, which is usually C:\Documents and Settings\{user name} on Windows 2000(32-bit), XP, and Server 2003(32-bit), or C:\Users\{user name} on Windows Vista, 7, 8, 8.1, 2008(64-bit), 2012(64-bit) and 10(64-bit).)

It drops the following files:

  • %System%\(random characters}
  • %User Temp%\hsperfdata_{username}\{process ID}
  • %User Temp%\{random characters}.xml
  • %User Profile%\.oracle_jre_usage\{random characters}.timestamp
  • %User Profile%\.ntusernt.ini
  • %User Profile%\bSBAJ\Desktop.ini
  • %User Profile%\Oracle\{copies of files under Java Installation folder}

(Note: %System% is the Windows system folder, where it usually is C:\Windows\System32 on all Windows operating system versions.. %User Temp% is the current user's Temp folder, which is usually C:\Documents and Settings\{user name}\Local Settings\Temp on Windows 2000(32-bit), XP, and Server 2003(32-bit), or C:\Users\{user name}\AppData\Local\Temp on Windows Vista, 7, 8, 8.1, 2008(64-bit), 2012(64-bit) and 10(64-bit).. %User Profile% is the current user's profile folder, which is usually C:\Documents and Settings\{user name} on Windows 2000(32-bit), XP, and Server 2003(32-bit), or C:\Users\{user name} on Windows Vista, 7, 8, 8.1, 2008(64-bit), 2012(64-bit) and 10(64-bit).)

It adds the following processes:

  • attrib +h %User Profile%\Oracle
  • attrib +h +r +s %User Profile%\.ntusernt.ini
  • attrib +s +r %User Profile%\bSBAJ\Desktop.ini
  • attrib +s +r %User Profile%\bSBAJ
  • attrib +h %User Profile%\bSBAJ
  • attrib +h +s +r %User Profile%\bSBAJ\rAbvl.class

(Note: %User Profile% is the current user's profile folder, which is usually C:\Documents and Settings\{user name} on Windows 2000(32-bit), XP, and Server 2003(32-bit), or C:\Users\{user name} on Windows Vista, 7, 8, 8.1, 2008(64-bit), 2012(64-bit) and 10(64-bit).)

It creates the following folders:

  • %User Profile%\Oracle
  • %User Profile%\bsBAJ
  • %User Profile%\.oracle_jre_usage
  • %User Temp%\hsperfdata_{username}

(Note: %User Profile% is the current user's profile folder, which is usually C:\Documents and Settings\{user name} on Windows 2000(32-bit), XP, and Server 2003(32-bit), or C:\Users\{user name} on Windows Vista, 7, 8, 8.1, 2008(64-bit), 2012(64-bit) and 10(64-bit).. %User Temp% is the current user's Temp folder, which is usually C:\Documents and Settings\{user name}\Local Settings\Temp on Windows 2000(32-bit), XP, and Server 2003(32-bit), or C:\Users\{user name}\AppData\Local\Temp on Windows Vista, 7, 8, 8.1, 2008(64-bit), 2012(64-bit) and 10(64-bit).)

Autostart Technique

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

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
RALOfXb = %User Profile%\Oracle\bin\javaw.exe -jar %User Profile%\bSBAJ\rAbvl.class

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\RunOnce
RALOfXb = %User Profile%\Oracle\bin\javaw.exe -jar %User Profile%\bSBAJ\rAbvl.class

Other System Modifications

This Backdoor deletes the following files:

  • %System%\{random characters}

(Note: %System% is the Windows system folder, where it usually is C:\Windows\System32 on all Windows operating system versions.)

It adds the following registry entries:

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Policies\
Attachments
SaveZoneInformation = 1

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Policies\
Associations
LowRiskFileTypes = .avi;.bat;.com;.cmd;.exe;.htm;.html;.lnk;.mpg;.mpeg;.mov;.mp3;.msi;.m3u;.rar;.reg;.txt;.vbs;.wav;.zip;.jar;

HKEY_LOCAL_MACHINE\SOFTWARE\Policies\
Microsoft\Windows NT\SystemRestore
DisableConfig = 1

HKEY_LOCAL_MACHINE\SOFTWARE\Policies\
Microsoft\Windows NT\SystemRestore
DisableSR = 1

HKEY_CURRENT_USER\Environment
SEE_MASK_NOZONECHECKS = 1

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Policies\
System
DisableTaskMgr = 2

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Control\Session Manager\Environment
SEE_MASK_NOZONECHECKS = 1

Other Details

This Backdoor connects to the following possibly malicious URL:

  • http://kaymaster.{BLOCKED}s.org

However, as of this writing, the said sites are inaccessible.

  SOLUTION

Minimum Scan Engine: 9.850
FIRST VSAPI PATTERN FILE: 15.662.04
FIRST VSAPI PATTERN DATE: 03 Feb 2020
VSAPI OPR PATTERN File: 15.663.00
VSAPI OPR PATTERN Date: 04 Feb 2020

Step 1

Before doing any scans, Windows 7, Windows 8, Windows 8.1, and Windows 10 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
    • RALOfXb = %User Profile%\Oracle\bin\javaw.exe -jar %User Profile%\bSBAJ\rAbvl.class
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\RunOnce
    • RALOfXb = %User Profile%\Oracle\bin\javaw.exe -jar %User Profile%\bSBAJ\rAbvl.class
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\Attachments
    • SaveZoneInformation = 1
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\Associations
    • LowRiskFileTypes = .avi;.bat;.com;.cmd;.exe;.htm;.html;.lnk;.mpg;.mpeg;.mov;.mp3;.msi;.m3u;.rar;.reg;.txt;.vbs;.wav;.zip;.jar;
  • In HKEY_CURRENT_USER\Environment
    • SEE_MASK_NOZONECHECKS = 1
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Environment
    • SEE_MASK_NOZONECHECKS = 1

Step 5

Restore this modified registry value

[ Learn More ]

Important: Editing the Windows Registry incorrectly can lead to irreversible system malfunction. Please do this only if you know how to or you can seek your system administrator’s help. You may also check out this Microsoft article first before modifying your computer's registry.

  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\System
    • From: DisableTaskMgr = 2
      To: DisableTaskMgr = 0
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows NT\SystemRestore
    • From: DisableConfig = 1
      To: DisableConfig = 0
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows NT\SystemRestore
    • From: DisableSR = 1
      To: DisableSR = 0

Step 6

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.
  • %User Profile%\Oracle
  • %User Profile%\bsBAJ
  • %User Profile%\.oracle_jre_usage
  • %User Temp%\hsperfdata_{username}

Step 7

Search and delete these files

[ 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.
  • %User Temp%\{random characters}.xml
  • %User Profile%\.ntusernt.ini

Step 8

Restart in normal mode and scan your computer with your Trend Micro product for files detected as Backdoor.Java.ADWIND.USMGBFDS. 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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