RANSOM_AVCRYPT.A

 Analysis by: Augusto II Remillano

 ALIASES:

Troj/AVCrypt-A(Sophos_Lite), Ransom:Win32/Pactelung.A (Microsoft)

 PLATFORM:

Windows

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

  • Threat Type: Ransomware

  • Destructiveness: No

  • Encrypted: No

  • In the wild: Yes

  OVERVIEW

Infection Channel:

Downloaded from the Internet

This Ransomware 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. It deletes itself after execution.

  TECHNICAL DETAILS

File Size:

3,052,032 bytes

File Type:

, EXE

Memory Resident:

Yes

Initial Samples Received Date:

26 Mar 2018

Payload:

Connects to URLs/IPs, Encrypts files, Displays message/message boxes

Arrival Details

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

  • %Application Data%\{User name}.exe

(Note: %Application Data% is the Application Data folder, where it usually is C:\Documents and Settings\{user name}\Application Data on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\AppData\Roaming on Windows Vista (32- and 64-bit), Windows 7 (32- and 64-bit), Windows 8 (32- and 64-bit), Windows 8.1 (32- and 64-bit), Windows Server 2008, and Windows Server 2012.)

It drops the following files:

  • %Application Data%\+{Random digits}.bmp - Wallpaper notifying the user that his/her data is encrypted
  • %User Temp%\+.bat - Cleans up the logs, processes and files created by the malware
  • %User Temp%\t.zip - an archive containing tor.exe and its components
  • libeay32.dll - Extracted from t.zip. DLL needed by tor
  • libevent_core-2-0-5.dll - Extracted from t.zip. DLL needed by tor
  • libevent_extra-2-0-5.dll - Extracted from t.zip. DLL needed by tor
  • libevent-2-0-5.dll - Extracted from t.zip. DLL needed by tor
  • libgcc_s_sjlj-1.dll - Extracted from t.zip. DLL needed by tor
  • libgmp-10.dll - Extracted from t.zip. DLL needed by tor
  • libssp-0.dll - Extracted from t.zip. DLL needed by tor
  • ssleay32.dll - Extracted from t.zip. DLL needed by tor
  • t.bmp - Extracted from t.zip. Will later be moved to %Application Data%\+{Random digits}.bmp
  • tor.exe - Extracted from t.zip. Used by malware to contact the C&C server
  • zlib1.dll - Extracted from t.zip. DLL needed by tor

(Note: %Application Data% is the Application Data folder, where it usually is C:\Documents and Settings\{user name}\Application Data on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\AppData\Roaming on Windows Vista (32- and 64-bit), Windows 7 (32- and 64-bit), Windows 8 (32- and 64-bit), Windows 8.1 (32- and 64-bit), Windows Server 2008, and Windows Server 2012.. %User Temp% is the user's temporary folder, where it usually is C:\Documents and Settings\{user name}\Local Settings\Temp on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\AppData\Local\Temp on Windows Vista (32- and 64-bit), Windows 7 (32- and 64-bit), Windows 8 (32- and 64-bit), Windows 8.1 (32- and 64-bit), Windows Server 2008, and Windows Server 2012.)

It adds the following processes:

  • tor.exe

It leaves text files that serve as ransom notes containing the following:

  • {Folders containing encrypted files}\+HOW_TO_UNLOCK.txt

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

  • .$

Autostart Technique

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

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Policies\
Explorer\Run
Windows = %Application Data%\{User name}.exe

HKEY_CURRENT_USER\SOFTWARE\Microsoft\
Windows\CurrentVersion\Policies\
Explorer\Run
Windows = %Application Data%\{User name}.exe

Other System Modifications

This Ransomware adds the following registry keys:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Uninstall\
Adobe
Default = ""

It modifies the following registry entries:

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Explorer\
Advanced
ShowInfoTip = 0

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Explorer\
Advanced
FolderContentsInfoTip = 0

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Explorer\
Advanced
EnableBalloonTips = 0

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
services\Winmgmt
Start = 2

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Explorer\
Advanced
StartButtonBalloonTip = 0

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Explorer\
Advanced
Hidden = 0

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Explorer\
Advanced
ShowSuperHidden = 0

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Explorer\
Advanced
HideSCAHealth = 1

HKEY_CURRENT_USER\Software\Microsoft\
Internet Explorer\Download
CheckExeSignatures = no

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Policies\
System
EnableVirtualization = 0

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Policies\
Associations
LowRiskFileTypes = .cmd;.exe;.bat;

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Explorer
SmartScreenEnabled = Off

HKEY_LOCAL_MACHINE\SOFTWARE\Policies\
Microsoft\Windows\System
EnableSmartScreen = 0

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Policies\
System
EnableLUA = 0

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\SystemRestore
RPSessionInterval = 0

HKEY_LOCAL_MACHINE\SOFTWARE\Policies\
Microsoft\Windows Defender\Real-Time Protection
DisableRealtimeMonitoring = 1

HKEY_LOCAL_MACHINE\SOFTWARE\Policies\
Microsoft\Windows Defender
DisableAntiSpyware = 1

HKEY_LOCAL_MACHINE\SOFTWARE\Policies\
Microsoft\Windows Defender\Real-Time Protection
DisableRealtimeMonitoring = 1

HKEY_LOCAL_MACHINE\SOFTWARE\Policies\
Microsoft\Windows\DeviceGuard
EnableVirtualizationBasedSecurity = 0

HKEY_LOCAL_MACHINE\SOFTWARE\Policies\
Microsoft\Windows\DeviceGuard
RequirePlatformSecurityFeatures = 0

HKEY_LOCAL_MACHINE\SOFTWARE\Policies\
Microsoft\Windows\DeviceGuard
HypervisorEnforcedCodeIntegrity = 0

HKEY_LOCAL_MACHINE\SOFTWARE\Policies\
Microsoft\Windows\DeviceGuard
HVCIMATRequired = 0

HKEY_LOCAL_MACHINE\SOFTWARE\Policies\
Microsoft\Windows\DeviceGuard
LsaCfgFlags = 0

It changes the desktop wallpaper by modifying the following registry entries:

HKEY_CURRENT_USER\Control Panel\Desktop
TileWallpaper = 0

HKEY_CURRENT_USER\Control Panel\Desktop
WallpaperStyle = 0

HKEY_CURRENT_USER\Control Panel\Desktop
Wallpaper = %Application Data%\+{Random digits}.bmp

It deletes the following registry keys:

HKEY_CURRENT_USER\Software\Policies\
Microsoft\Windows\System
DisableCMD = 0

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

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Policies\
System
DisableRegistryTools = 0

Backdoor Routine

This Ransomware posts the following information to its command and control (C&C) server:

  • Windows version
  • Time zone

Other Details

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

  • https://www.microsoft.com

It connects to the following possibly malicious URL:

  • {BLOCKED}uupc.onion

It does the following:

  • It sets the machine's desktop to the following:
  • Deletes backup catalog of the affected machine by executing the following command:
    • wbadmin delete catalog -quiet
  • It deletes shadow copies by executing the following command:
    • wmic shadowcopy delete /nointeractive
  • Acquires a list of antivirus products installed in the system through the following WQL data query:
    • SELECT * FROM AntiVirusProduct
  • Uninstalls any antivirus product installed in the system via the following command
    • wmic product where ( Vendor like "%{AV product name}%" ) call uninstall /nointeractive
  • It deletes services by executing the following commands:
    • sc config config "MBAMService" start= disabled
    • sc config stop "MBAMService"
    • sc config delete "MBAMService"
    • sc config config "MBAMSwissArmy " start= disabled
    • sc config stop "MBAMSwissArmy "
    • sc config delete "MBAMSwissArmy "
    • sc config config "MBAMChameleon " start= disabled
    • sc config stop "MBAMChameleon "
    • sc config delete "MBAMChameleon "
    • sc config config "MBAMWebProtection" start= disabled
    • sc config stop "MBAMWebProtection"
    • sc config delete "MBAMWebProtection"
    • sc config config "MBAMFarflt" start= disabled
    • sc config stop "MBAMFarflt"
    • sc config delete "MBAMFarflt"
    • sc config config "ESProtectionDriver" start= disabled
    • sc config stop "ESProtectionDriver"
    • sc config delete "ESProtectionDriver"
    • sc config config "MBAMProtection" start= disabled
    • sc config stop "MBAMProtection"
    • sc config delete "MBAMProtection"
    • sc config config "Schedule" start= disabled
    • sc config stop "Schedule"
    • sc config delete "Schedule"
    • sc config config "WPDBusEnum" start= disabled
    • sc config stop "WPDBusEnum"
    • sc config delete "WPDBusEnum"
    • sc config config "TermService" start= disabled
    • sc config stop "TermService"
    • sc config delete "TermService"
    • sc config config "SDRSVC" start= disabled
    • sc config stop "SDRSVC"
    • sc config delete "SDRSVC"
    • sc config config "RasMan" start= disabled
    • sc config stop "RasMan"
    • sc config delete "RasMan"
    • sc config config "PcaSvc" start= disabled
    • sc config stop "PcaSvc"
    • sc config delete "PcaSvc"
    • sc config config "MsMpSvc" start= disabled
    • sc config stop "MsMpSvc"
    • sc config delete "MsMpSvc"
    • sc config config "SharedAccess" start= disabled
    • sc config stop "SharedAccess"
    • sc config delete "SharedAccess"
    • sc config config "wscsvc" start= disabled
    • sc config stop "wscsvc"
    • sc config delete "wscsvc"
    • sc config config "srservice" start= disabled
    • sc config stop "srservice"
    • sc config delete "srservice"
    • sc config config "Schedule" start= disabled
    • sc config stop "Schedule"
    • sc config delete "Schedule"
    • sc config config "VSS" start= disabled
    • sc config stop "VSS"
    • sc config delete "VSS"
    • sc config config "swprv" start= disabled
    • sc config stop "swprv"
    • sc config delete "swprv"
    • sc config config "WerSvc" start= disabled
    • sc config stop "WerSvc"
    • sc config delete "WerSvc"
    • sc config config "MpsSvc" start= disabled
    • sc config stop "MpsSvc"
    • sc config delete "MpsSvc"
    • sc config config "WinDefend" start= disabled
    • sc config stop "WinDefend"
    • sc config delete "WinDefend"
    • sc config config "wuauserv" start= disabled
    • sc config stop "wuauserv"
    • sc config delete "wuauserv"
  • Changes the affected machine’s boot configuration by executing the following commands:
    • bcdedit /timeout 0
    • bcdedit /set {bootmgr} displaybootmenu no
    • bcdedit /set {default} bootems off
    • bcdedit /set {default} advancedoptions off
    • bcdedit /set {default} optionsedit off
    • bcdedit /set {default} bootstatuspolicy ignoreallfailures
    • bcdedit /set {default} recoveryenabled No
  • It avoids encrypting files with the following extensions:
    • .kdmp
    • .lnk
    • .manifest
    • .mkv
    • .mp3
    • .msi
    • .png
    • .sam
    • .scr
    • .sys
    • .temp
    • .theme
    • .ttf
    • .url
    • .vdx
    • .vxd
    • .wav
    • .wim
    • .avi
    • .bat
    • .cab
    • .chm
    • .cmd
    • .com
    • .cpl
    • .dll
    • .dmp
    • .evtx
    • .exe
    • .flv
    • .folder
    • .gif
    • .ico
    • .inf
    • .ini

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

It deletes itself after execution.

It does not proceed to its malicious routine if it detects that it is being debugged.

Ransomware Routine

This Ransomware avoids encrypting files found in the following folders:

  • drm
  • sendto
  • i386
  • perl
  • boost
  • config.msi
  • system volume information
  • programfiles(x86)
  • windows
  • appdata
  • programdata
  • programfiles
  • $recycle.bin
  • windows.old
  • $windows.~bt
  • driver
  • boot
  • winsxs
  • driverstore
  • cache2
  • httpcache
  • cookieshistory
  • ie5
  • internet explorer
  • firefox
  • chrome
  • opera
  • content.ie5
  • node_modules
  • applicationdata
  • nvidia
  • intel
  • microsoft
  • music
  • song
  • sample pictures
  • sample videos
  • sample media
  • local settings
  • prefetch
  • winnt
  • readme
  • spider
  • preflogs
  • recycle
  • recycler
  • movies
  • cookies
  • localservice
  • default
  • xampp

It renames encrypted files using the following names:

  • +{original file name}

It leaves text files that serve as ransom notes containing the following text:

  • lol n

  SOLUTION

Minimum Scan Engine:

9.850

FIRST VSAPI PATTERN FILE:

14.152.04

FIRST VSAPI PATTERN DATE:

26 Mar 2018

VSAPI OPR PATTERN File:

14.153.00

VSAPI OPR PATTERN Date:

27 Mar 2018

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\Policies\Explorer\Run
    • Windows = %Application Data%\{User name}.exe
  • In HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\Explorer\Run
    • Windows = %Application Data%\{User name}.exe
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\Associations
    • LowRiskFileTypes = .cmd;.exe;.bat;

Step 5

Delete this registry key

[ 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\Uninstall\Adobe
    • Default = ""

Step 6

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_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced
    • ShowInfoTip = 1
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced
    • FolderContentsInfoTip = 1
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced
    • EnableBalloonTips = 1
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced
    • StartButtonBalloonTip = 1
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced
    • Hidden = 1
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced
    • ShowSuperHidden = 1
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced
    • HideSCAHealth = 0
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows Defender\Real-Time Protection
    • DisableRealtimeMonitoring = 0
  • In HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\Download
    • CheckExeSignatures = yes
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\System
    • EnableVirtualization = 1
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows Defender
    • DisableAntiSpyware = 0
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows Defender\Real-Time Protection
    • DisableRealtimeMonitoring = 0
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer
    • SmartScreenEnabled = On
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows\System
    • EnableSmartScreen = 1
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\System
    • EnableLUA = 1
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\SystemRestore
    • RPSessionInterval = 1
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows\DeviceGuard
    • EnableVirtualizationBasedSecurity = 1
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows\DeviceGuard
    • RequirePlatformSecurityFeatures = 1
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows\DeviceGuard
    • HypervisorEnforcedCodeIntegrity = 1
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows\DeviceGuard
    • HVCIMATRequired = 1
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows\DeviceGuard
    • LsaCfgFlags = 1

Step 7

Reset your Desktop properties

[ Learn More ]

Step 8

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.
  • %User Temp%\libeay32.dll
  • %User Temp%\libevent_core-2-0-5.dll
  • %User Temp%\libevent_extra-2-0-5.dll
  • %User Temp%\libevent-2-0-5.dll
  • %User Temp%\libgcc_s_sjlj-1.dll
  • %User Temp%\libgmp-10.dll
  • %User Temp%\libssp-0.dll
  • %User Temp%\ssleay32.dll
  • %User Temp%\t.bmp
  • %User Temp%\tor.exe
  • %User Temp%\zlib1.dll
  • %User Temp%\t.zip
  • %Application Data%\+{Random digits}.bmp
  • %User Temp%\+.bat
  • {Folders containing encrypted files}\+HOW_TO_UNLOCK.txt

Step 9

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

Restore encrypted files from backup.

NOTES:

Enable Windows Recovery Option:

  1. Run cmd.exe as administrator.
  2. Type bcdedit /timeout 30 then press Enter.
  3. Type bcdedit /set {bootmgr} displaybootmenu yes then press Enter.
  4. Type bcdedit /set {default} bootems on then press Enter.
  5. Type bcdedit /set {default} advancedoptions on then press Enter.
  6. Type bcdedit /set {default} optionsedit on then press Enter.
  7. Type bcdedit /set {default} recoveryenabled yes then press Enter.

Restoring Services Deleted by the Malware

  1. sc create "{Service Name}" binpath= {Service Path} start= auto
  2. sc start "{Service Name}"


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