RANSOM_CRYPTESLA.CBQ1635

 Analysis by: Francis Xavier Antazo

 ALIASES:

Ransom:Win32/Tescrypt!rfn (Microsoft); Win32/Filecoder.TeslaCrypt.I trojan (ESET); Trojan horse FileCryptor.IAA (AVG);

 PLATFORM:

Windows

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

  • Threat Type: Trojan

  • Destructiveness: No

  • Encrypted: Yes

  • 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 modifies the Internet Explorer Zone Settings.

It connects to certain websites to send and receive information. It gathers information and reports it to its servers.

  TECHNICAL DETAILS

File Size:

376,832 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

04 Mar 2016

Payload:

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

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:

  • %Windows%\{random filename}.exe

(Note: %Windows% is the Windows folder, where it usually is C:\Windows on all Windows operating system versions.)

It drops the following component file(s):

  • {folders containing encrypted files}\_ReCoVeRy_+{random}.png - ransom note
  • {folders containing encrypted files}\_ReCoVeRy_+{random}.html - ransom note
  • {folders containing encrypted files}\_ReCoVeRy_+{random}.txt - ransom note
  • %My Documents%\_ReCoVeRy_+{random}.html - ransom note
  • %My Documents%\_ReCoVeRy_+{random}.txt - ransom note
  • %My Documents%\recover_file_{random}.txt - ransom note

    (Note: %My Documents% is usually C:\Documents and Settings\{user name}\My Documents on Windows 2000, XP, and Server 2003, or C:\Users\{user name}\Documents on Windows Vista and 7.)

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\Run
{random} = "C:\Windows\system32\CMD.EXE /c start %Windows%\{random filename}.exe"

Other System Modifications

This Trojan adds the following registry keys:

HKEY_CURRENT_USER\Software\zzzsys

HKEY_CURRENT_USER\Software\{ID}

It adds the following registry entries:

HKEY_CURRENT_USER\Software\zzzsys
ID = "{ID}"

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Policies\
System
EnableLinkedConnections = "1"

It modifies the following registry entries:

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Internet Settings
ProxyServer = "http=127.0.0.1:8888;https=127.0.0.1:8888;"

(Note: The default value data of the said registry entry is {user-defined}.)

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Internet Settings
ProxyOverride = "<-loopback>"

(Note: The default value data of the said registry entry is {user-defined}.)

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Internet Settings
ProxyEnable = "1"

(Note: The default value data of the said registry entry is {user-defined}.)

Web Browser Home Page and Search Page Modification

This Trojan modifies the Internet Explorer Zone Settings.

Other Details

This Trojan connects to the following website to send and receive information:

  • http://{BLOCKED}tecnicos.com/media/editors/wstr.php
  • http://{BLOCKED}ctivo.com/wstr.php
  • http://{BLOCKED}rnal.com/pmtsys/fonts/wstr.php
  • http://{BLOCKED}yeli.com/wstr.php
  • http://{BLOCKED}online.com/wstr.php
  • http://{BLOCKED}turemediablog.com/wp-includes/fonts/wstr.php

It encrypts files with the following extensions:

  • .7z
  • .accdb
  • .apk
  • .arch00
  • .asset
  • .avi
  • .bak
  • .bar
  • .bc6
  • .bc7
  • .big
  • .bik
  • .bkf
  • .bkp
  • .blob
  • .bsa
  • .cas
  • .cfr
  • .css
  • .csv
  • .d3dbsp
  • .das
  • .dazip
  • .db0
  • .dba
  • .desc
  • .dmp
  • .docm
  • .dwg
  • .dxg
  • .epk
  • .erf
  • .esm
  • .ff
  • .flv
  • .forge
  • .fos
  • .fpk
  • .fsh
  • .gdb
  • .gho
  • .hkdb
  • .hkx
  • .hplg
  • .hvpl
  • .ibank
  • .icxs
  • .itdb
  • .itl
  • .itm
  • .itm
  • .iwd
  • .iwi
  • .jpeg
  • .js
  • .kdb
  • .kf
  • .layout
  • .lbf
  • .litemod
  • .litesql
  • .lrf
  • .ltx
  • .lvl
  • .m2
  • .m3u
  • .m4a
  • .map
  • .mcmeta
  • .mdb
  • .mdbackup
  • .mddata
  • .menu
  • .mlx
  • .mov
  • .mp4
  • .mpqge
  • .ncf
  • .ntl
  • .p12
  • .p7b
  • .p7c
  • .pak
  • .pfx
  • .pkpass
  • .png
  • .ppt
  • .pptm
  • .pptx
  • .psk
  • .pst
  • .py
  • .qdf
  • .qic
  • .raf
  • .rar
  • .rb
  • .re4
  • .rgss3a
  • .rim
  • .rofl
  • .rtf
  • .sav
  • .sb
  • .sb
  • .sid
  • .sidd
  • .sidn
  • .sie
  • .sis
  • .slm
  • .snx
  • .sql
  • .sum
  • .svg
  • .syncdb
  • .t12
  • .t13
  • .tax
  • .tiff
  • .tor
  • .txt
  • .upk
  • .vcf
  • .vdf
  • .vfs0
  • .vpk
  • .vpp_pc
  • .vtf
  • .w3x
  • .wb2
  • .wma
  • .wmo
  • .wmo
  • .wmv
  • .wpd
  • .wps
  • .xf
  • .xlk
  • .xls
  • .xlsb
  • .xlsm
  • .xlsx
  • .xxx
  • .zip
  • .ztmp

It gathers the following information and reports it to its servers:

  • Total size of encrypted files
  • OS information
  • Installation ID

NOTES:

This malware encrypts files in all fixed, removable, and network drives and shares.

It deletes shadow copies by executing the following command:

WMIC.exe shadowcopy delete /nointeractive

It terminates processes containing the following strings:

  • askmg
  • cmd
  • egedi
  • rocex
  • sconfi

It appends the extension .mp3 to the file name of the encrypted files. It avoids encrypting files found in the following folders:

  • Windows
  • Program Files
  • %All Users Profile%\Application Data - if infected system is running Windows XP or older versions
  • ProgramData - if infected system is running Windows Vista or newer versions

It opens ransom notes after its encryption routine.

  SOLUTION

Minimum Scan Engine:

9.800

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

Scan your computer with your Trend Micro product and note files detected as RANSOM_CRYPTESLA.CBQ1635

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
    • {random} = "C:\Windows\system32\CMD.EXE /c start %Windows%\{random filename}.exe"
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\System
    • EnableLinkedConnections = "1"

Step 6

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_CURRENT_USER\Software
    • zzzsys
  • In HKEY_CURRENT_USER\Software
    • {ID}

Step 7

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\Internet Settings
    • From: ProxyEnable = "1"
      To: ProxyEnable = "{user-defined}"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Internet Settings
    • From: ProxyServer = "http=127.0.0.1:8888;https=127.0.0.1:8888;"
      To: ProxyServer = "{user-defined}"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Internet Settings
    • From: ProxyOverride = "<-loopback>"
      To: ProxyOverride = "{user-defined}"

Step 8

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.
  • _ReCoVeRy_+{random}.png
  • _ReCoVeRy_+{random}.html
  • _ReCoVeRy_+{random}.txt
  • recover_file_{random}.txt

Step 9

Restart in normal mode and scan your computer with your Trend Micro product for files detected as RANSOM_CRYPTESLA.CBQ1635. 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.


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