Ransom.Win32.SCHOOBOS.A

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.

It avoids encrypting files with the following file extensions.

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 files:

• %ProgramData%\exxga8oKd.ico → icon used for all encrypted files.
• %ProgramData%\exxga8oKd.bmp → image to set as system wallpaper after encryption

(Note: %ProgramData% is a version of the Program Files folder where any user on a multi-user computer can make changes to programs. This contains application data for all users. This is usually C:\ProgramData on Windows Vista, 7, 8, 8.1, 2008(64-bit), 2012(64-bit) and 10(64-bit), or C:\Documents and Settings\All Users on Windows Server 2003(32-bit), 2000(32-bit) and XP.)

It adds the following processes:

• bcdedit /set {current} safeboot network → if -safe commandline parameter is used

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

• Global\3620d3a865322698b9aafc9c1d227fe9

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\RunOnce → if -safe commandline parameter is used
{Random Characters} = {Malware Path}\{Malware File Name}

Other System Modifications

This Ransomware modifies the following registry entries:

HKEY_LOCAL_MACHINE\SOFTWARE\Classes\
.exxga8oKd
(Defaut) = exxga8oKd

HKEY_LOCAL_MACHINE\SOFTWARE\Classes\
exxga8oKd\DefaultIcon
(Defaut) = %ProgramData%\exxga8oKd.ico

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Explorer
GlobalAssocChangedCounter = 38

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\Winlogon → if -safe commandline parameter is used
AutoAdminLogon = 1

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\Winlogon → if -safe commandline parameter is used
DefaultUserName = Administrator

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\Winlogon → if -safe commandline parameter is used
DefaultDomainName = {Computer Domain Name}

HKEY_LOCAL_MACHINE\SOFTWARE\Classes\
exxga8oKd → if -safe commandline parameter is used
hScreen = 928

HKEY_LOCAL_MACHINE\SOFTWARE\Classes\
exxga8oKd → if -safe commandline parameter is used
wScreen = 1918

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

HKEY_CURRENT_USER\Control Panel\Desktop
WallPaper = %ProgramData%\exxga8oKd.bmp

HKEY_CURRENT_USER\Control Panel\Desktop
WallpaperStyle = 10

HKEY_CURRENT_USER\Control Panel\Desktop
Wallpaper = %ProgramData%\exxga8oKd.bmp

It sets the system's desktop wallpaper to the following image:

File Infection

This Ransomware avoids infecting files that contain the following strings in their names:

• autorun.inf
• boot.ini
• bootfont.bin
• bootsect.bak
• desktop.ini
• iconcache.db
• ntldr
• ntuser.dat
• ntuser.dat.log
• ntuser.ini
• thumbs.db

Process Termination

This Ransomware terminates the following services if found on the affected system:

• vss
• sql
• svc$
• memtas
• mepocs
• msexchange
• sophos
• veeam
• backup
• GxVss
• GxBlr
• GxFWD
• GxCVD
• GxCIMgr

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

• sql
• oracle
• ocssd
• dbsnmp
• synctime
• agntsvc
• isqlplussvc
• xfssvccon
• mydesktopservice
• ocautoupds
• encsvc
• firefox
• tbirdconfig
• mydesktopqos
• ocomm
• dbeng50
• sqbcoreservice
• excel
• infopath
• msaccess
• mspub
• onenote
• outlook
• powerpnt
• steam
• thebat
• thunderbird
• visio
• winword
• wordpad
• notepad
• calc
• wuauclt
• onedrive

Information Theft

This Ransomware accepts the following parameters:

• -safe →Reboots in safeboot, then encrypts the user's machine
• -wall → Changes system Wallpaper and Print ransom note on printers then deletes itself after renaming for 26 times.
• -path {target} → Specifically encrypt the target, can be file or folder
• -gspd → Perform Group Policy Modification for Lateral Movement
• -psex → Lateral Movement via Admin Shares
• -gdel → Delete group policy updates
• -del → Deletes itself after renaming for 26 times.

Other Details

This Ransomware adds the following registry keys:

HKEY_LOCAL_MACHINE\SOFTWARE\Classes\
.exxga8oKd

HKEY_LOCAL_MACHINE\SOFTWARE\Classes\
exxga8oKd

HKEY_LOCAL_MACHINE\SOFTWARE\Classes\
exxga8oKd\DefaultIcon

It does the following:

• If not executed with admin rights, it will attempt to relaunch itself as admin by elevating its privileges via bypassing UAC
• It encrypts fixed, removable and network shares
• It deletes files in recycle bin folder for removable and fixed drives
• It uses WQL to delete shadow copies
• It renames itself 26 times before deleting itself after encryption
• It has the capability to print the ransom note in infected machines
• It terminates if the machine has the following system language:
• Arabic (Syria)
• Armenian (Armenia)
• Azerbaijani (Cyrillic Azerbaijan)
• Azerbaijani (Latin Azerbaijan)
• Belarusian (Belarus)
• Georgian (Georgia)
• Kazakh (Kazakhstan)
• Kyrgyz (Kyrgyzstan)
• Russian (Moldova)
• Russian (Russia)
• Tajik (Cyrillic Tajikistan)
• Tatar (Russia) Romanian (Moldova)
• Turkmen (Turkmenistan)
• Ukranian (Ukraine)
• Uzbek (Cyrillic Uzbekistan)
• Uzbek (Latin Uzbekistan)
• It deletes the following services with corresponding hashes:
• 0xE3823BF2
• 0xE42EE5F5
• 0xC46F5935
• 0xE1D75A35 → wdnissvc
• 0xB7BA4173 → WinDefend
• 0x6AFA4DBA → wscsvc
• 0xEAEB1DB8 → sppsvc
• 0x5F2E6CFA → Sense
• 0x616E5B6A → SecurityHealthService

Ransomware Routine

This Ransomware avoids encrypting files found in the following folders:

• $recycle.bin
• $windows.~bt
• $windows.~ws
• all users
• appdata
• application data
• boot
• config.msi
• default
• google
• intel
• mozilla
• msocache
• perflogs
• program files
• program files (x86)
• programdata
• public
• system volume information
• tor browser
• windows
• windows.old
• x64dbg

It appends the following extension to the file name of the encrypted files:

• .exxga8oKd

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

• %Desktop%\exxga8oKd.README.txt
• {Encrypted Directory}\exxga8oKd.README.txt
  

It avoids encrypting files with the following file extensions:

• 386
• adv
• ani
• bat
• bin
• cab
• cmd
• com
• cpl
• cur
• deskthemepack
• diagcab
• diagcfg
• diagpkg
• dll
• drv
• exe
• hlp
• hta
• icl
• icns
• ico
• ics
• idx
• key
• ldf
• lnk
• lock
• mod
• mpa
• msc
• msi
• msp
• msstyles
• msu
• nls
• nomedia
• ocx
• pdb
• prf
• ps1
• rom
• rtp
• scr
• shs
• spl
• sys
• theme
• themepack
• wpx