Analysis by: Arianne Grace Dela Cruz
ALIASES:

Ransom:Win32/RookCrypt.PA!MTB (MICROSOFT); Win64/Filecoder.Rook.A trojan (NOD32)

 PLATFORM:

Windows

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

  • Threat Type: Ransomware

  • Destructiveness: No

  • Encrypted: Yes

  • 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.

It executes then deletes itself afterward.

It drops files as ransom note. It avoids encrypting files with the following file extensions.

  TECHNICAL DETAILS

File Size: 174,080 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 31 Dec 2021
Payload: Displays message/message boxes, Encrypts files, Disables services, Terminates processes

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 adds the following processes:

  • cmd.exe /c vssadmin.exe delete shadows /all /quiet

It executes then deletes itself afterward.

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

  • asfgjkl878645165456fa888

Other System Modifications

This Ransomware adds the following registry entries as part of its installation routine:

HKEY_CURRENT_USER\Software
RookPrivateKey = {Hex Values}

HKEY_CURRENT_USER\Software
RookPublicKey = {Hex Values}

Process Termination

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

  • AcronisAgent
  • AcrSch2Svc
  • backup
  • CAARCUpdateSvc
  • CASAD2DWebSvc
  • ccEvtMgr
  • ccSetMgr
  • DefWatch
  • GxBlr
  • GxCIMgr
  • GxCVD
  • GxFWD
  • GxVss
  • Intuit.QuickBooks.FCS
  • memtas
  • mepocs
  • QBCFMonitorService
  • QBFCService
  • QBIDPService
  • RTVscan
  • SavRoam
  • sql
  • svc$
  • veeam
  • vss

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

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

Other Details

This Ransomware does the following:

  • It empties the Recycle Bin.
  • It encrypts files from the local drives and network shares.
  • It uses Windows Restart Manager to unlock files it will encrypt.
  • It renames the malware to "{Malware Name}:ask" during execution.

It accepts the following parameters:

  • -debug {log file name} - for logging
  • -shares {network shares to encrypt} - encrypt specified network shares
  • -paths {drives to encrypt} - encrypt specified drives

Ransomware Routine

This Ransomware avoids encrypting files with the following strings in their file path:

  • #recycle
  • $Recycle Bin
  • All Users
  • AppData
  • autorun.inf
  • Boot
  • boot.ini
  • bootfont.bin
  • bootmgfw.efi
  • bootmgr
  • bootmgr.efi
  • bootsect.bak
  • desktop.ini
  • Google
  • iconcache.db
  • Internet Explorer
  • Mozilla
  • Mozilla Firefox
  • ntldr
  • ntuser.dat
  • ntuser.dat.log
  • ntuser.ini.
  • Opera
  • Opera Software
  • Program Files
  • Program Files (x86)
  • ProgramData
  • thumbs.db
  • Tor Browser
  • Windows
  • Windows.old
  • HowToRestoreYourFiles.txt
  • {Log file name}

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

  • .Rook

It drops the following file(s) as ransom note:

  • {Encrypted Directory}\HowToRestoreYourFiles.txt

It avoids encrypting files with the following file extensions:

  • .exe
  • .dll
  • .Rook

  SOLUTION

Minimum Scan Engine: 9.800
FIRST VSAPI PATTERN FILE: 17.292.04
FIRST VSAPI PATTERN DATE: 03 Jan 2022
VSAPI OPR PATTERN File: 17.293.00
VSAPI OPR PATTERN Date: 04 Jan 2022

Step 1

Trend Micro Predictive Machine Learning detects and blocks malware at the first sign of its existence, before it executes on your system. When enabled, your Trend Micro product detects this malware under the following machine learning name:

     Troj.Win32.TRX.XXPE50FFF051

Step 2

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 3

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 4

Restart in Safe Mode

[ Learn More ]

Step 5

Delete these registry values

[ 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
    • RookPrivateKey = {Hex Values}
  • In HKEY_CURRENT_USER\Software
    • RookPublicKey = {Hex Values}

Step 6

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.
  • {Encrypted Directory}\HowToRestoreYourFiles.txt

Step 7

Restart in normal mode and scan your computer with your Trend Micro product for files detected as Ransom.Win64.ROOK.YXCAC. 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 8

Restore encrypted files from backup.


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