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RANSOM_CRYPTESLA.XXF

August 20, 2015
 ALIASES:

Ransom:Win32/Tescrypt.A (Microsoft)

 PLATFORM:

Windows

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

  • Threat Type: Trojan

  • Destructiveness: No

  • Encrypted:

  • In the wild: Yes

  OVERVIEW

Infection Channel:

Downloaded from the Internet

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

It deletes the initially executed copy of itself.

  TECHNICAL DETAILS

File Size:

256,215 bytes

File Type:

EXE

Memory Resident:

No

Initial Samples Received Date:

14 Aug 2015

Payload:

Connects to URLs/IPs, Encrypts files

Arrival Details

This Trojan 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 Trojan drops the following copies of itself into the affected system and executes them:

  • %Application Data%\vcw{3 random letters}.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:

  • %User Profile%\My Documents\Recovery_File_{random 5 letters 1}.txt
  • %Desktop%\RESTORE_FILES.HTML
  • %Desktop%\RESTORE_FILES.TXT
  • %Desktop%\RESTORE_FILES.BMP

(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.. %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.)

Autostart Technique

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

HKEY_CURRENT_USER\SOFTWARE\Microsoft\
Windows\CurrentVersion\RunOnce
MSCONFIG = "%Application Data%\vcw{random letters}.exe"

Other System Modifications

This Trojan adds the following registry entries:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\policies\
system
EnabledLinkConnections = 1

HKEY_CURRENT_USER\Software\{installation ID}
data = {encryption information}

HKEY_CURRENT_USER\Software\msys
ID = {installation ID}

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Run
MSCONFIG = "C"

Other Details

This Trojan connects to the following URL(s) to get the affected system's IP address:

  • ipinfo.io/ip

It connects to the following possibly malicious URL:

  • http://{BLOCKED}erheath.ru/{path}/{encoded information}
  • http://{BLOCKED}notube.org/{path}/{encoded information}
  • http://{BLOCKED}tynowbooksandgifts.com/{path}/{encoded information}
  • http://{BLOCKED}ppen.nl/{path}/{encoded information}
  • http://{BLOCKED}erests.com/{path}/{encoded information}
  • http://{BLOCKED}almarketing.com/{path}/{encoded information}

It deletes the initially executed copy of itself

NOTES:

The variable {path} can be any of the following:

  • /wp-content/themes/r.php?
  • /inst.php?

It drops restore_files_{random 5 letters 2}.html and restore_files_{random 5 letters 2}.txt in all folders it traversed.

  SOLUTION

Minimum Scan Engine:

9.750

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

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\system
    • EnabledLinkConnections = 1
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
    • MSCONFIG = "C"
  • In HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
    • MSCONFIG = "%Application Data%\vcw{random letters}.exe"
  • In HKEY_CURRENT_USER\Software\{installation ID}
    • data = {encryption information}
  • In HKEY_CURRENT_USER\Software\msys
    • ID = {installation ID}

Step 4

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.
  • %Desktop%\RESTORE_FILES.HTML
  • %Desktop%\RESTORE_FILES.TXT
  • %Desktop%\RESTORE_FILES.BMP
  • restore_files_{random 5 letters 2}.html
  • restore_files_{random 5 letters 2}.txt

Step 5

Scan your computer with your Trend Micro product to delete files detected as RANSOM_CRYPTESLA.XXF. 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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