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RANSOM_CRYPTOJOKER.B

February 15, 2018
 Analysis by: Christian Noel Olalia
 ALIASES:

Trojan-Ransom.Win32.Crypmod.ykx (KASPERSKY); Ransom.Enciphered (NORTON); Ransom:MSIL/CryptJoke.B!bit [non_writable_container] (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:

Dropped by other malware, 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 encrypts files found in specific folders. It drops files as ransom note.

  TECHNICAL DETAILS

File Size:

581,120 bytes

File Type:

, EXE

Memory Resident:

Yes

Initial Samples Received Date:

09 Jul 2017

Payload:

Drops files, Displays message/message boxes, Encrypts files

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.

Autostart Technique

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

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
Sound Card = %Desktop%\CryptoJokerDecryptor.exe

Other Details

This Ransomware drops the following file(s)/component(s):

  • %Application Data%\encKey.cryptojoker - contains encryption key
  • %Application Data%\jokingwithyou.cryptojoker - necessary for decryption process
  • %Desktop%\CryptoJokerDecryptor.exe - decryptor containing ransom note

(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.. %Desktop% is the desktop folder, where it usually is C:\Documents and Settings\{user name}\Desktop in Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\Desktop in 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 does the following:

  • CryptoJokerDecryptor.exe displays the following:
  • The malware would terminate upon finding a running process during encryption routine and would display the following at command prompt:

Ransomware Routine

This Ransomware encrypts files found in the following folders:

  • %User Profile%\

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

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

  • .partially.cryptojoker
  • .fully.cryptojoker

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

  • %Desktop%\CryptoJoker Recovery Information.txt

  SOLUTION

Minimum Scan Engine:

9.850

FIRST VSAPI PATTERN FILE:

13.538.04

FIRST VSAPI PATTERN DATE:

17 Jul 2017

VSAPI OPR PATTERN File:

13.539.00

VSAPI OPR PATTERN Date:

18 Jul 2017

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

Identify and terminate files detected as RANSOM_CRYPTOJOKER.B

[ Learn More ]
  1. Windows Task Manager may not display all running processes. In this case, please use a third-party process viewer, preferably Process Explorer, to terminate the malware/grayware/spyware file. You may download the said tool here.
  2. If the detected file is displayed in either Windows Task Manager or Process Explorer but you cannot delete it, restart your computer in safe mode. To do this, refer to this link for the complete steps.
  3. If the detected file is not displayed in either Windows Task Manager or Process Explorer, continue doing the next steps.

Step 4

Restart in Safe Mode

[ Learn More ]

Step 5

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
    • Sound Card = %Desktop%\CryptoJokerDecryptor.exe

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.
  • %Application Data%\encKey.cryptojoker
  • %Application Data%\jokingwithyou.cryptojoker
  • %Desktop%\CryptoJokerDecryptor.exe
  • %Desktop%\CryptoJoker Recovery Information.txt

Step 7

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