RANSOM_CRYPWALL.UAS

December 01, 2015
 Analysis by: Homer Pacag
 ALIASES:

Trojan.Phonywall (Symantec)

 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.

  TECHNICAL DETAILS

File Size:

363,008 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

25 Nov 2015

Payload:

Encrypts files, Displays graphics/image

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 files:

  • %All Users Profile%\Desktop\DECRYPT_INSTRUCTION.html - the ransom note
  • %Desktop%\DECRYPT_INSTRUCTION.html - the ransom note

(Note: %All Users Profile% is the All Users folder, where it usually is C:\Documents and Settings\All Users on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\ProgramData 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 drops the following copies of itself into the affected system:

  • %All Users Profile%\Application Data\Microsoft\Windows\{Malware Name}.exe

(Note: %All Users Profile% is the All Users folder, where it usually is C:\Documents and Settings\All Users on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\ProgramData 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 creates the following folders:

  • %All Users Profile%\Application Data\Microsoft\Windows

(Note: %All Users Profile% is the All Users folder, where it usually is C:\Documents and Settings\All Users on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\ProgramData 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.)

Autostart Technique

This Trojan registers itself as a system service to ensure its automatic execution at every system startup by adding the following registry entries:

HKLM\SYSTEM\ControlSet001\
Services\{Malware Name}
ImagePath = "%All Users Profile%\Application Data\Microsoft\Windows\6640.exe" -run 1

HKLM\SYSTEM\ControlSet001\
Services\{Malware Name}
DisplayName = Check Disk Service

HKLM\SYSTEM\ControlSet001\
Services\{Malware Name}
Description = Creates and displays a status report for a disk based on the file system. Chkdsk also lists and corrects errors on the disk.

NOTES:

This malware only runs if the following parameters are supplied in execution:

  • run
  • install

It encrypts files as is - same file size, same file name,and same file icon. It avoids encrypting files if the following strings are present in the file name and/or extension:

  • *.com
  • *.dll
  • *.exe
  • *.inf
  • *.lnk
  • *.msi
  • *.msu
  • *.ocx
  • *.scr
  • *.sys
  • boot.ini
  • bootmgr
  • ntldr
  • ntuser.*

It avoids these folders if following strings are present in the folder name:

  • Boot
  • Windows
  • Program Files*
  • System Volume Information

It terminates processes if the running process contains the following strings:

  • *exchange*
  • *exfba*
  • *fdlauncher*
  • *iis*
  • *inet*
  • *mad*
  • *msdtssrvr*
  • *ReportingServicesService*
  • *sql*
  • *store*
  • *w3wp*

It displays this ransom note:

  SOLUTION

Minimum Scan Engine:

9.800

FIRST VSAPI PATTERN FILE:

12.172.06

FIRST VSAPI PATTERN DATE:

25 Nov 2015

VSAPI OPR PATTERN File:

12.173.00

VSAPI OPR PATTERN Date:

26 Nov 2015

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

Restart in Safe Mode

[ Learn More ]

Step 4

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.

 
  • HKLM\SYSTEM\ControlSet001\Services\{Malware Name}

Step 5

Search and delete this file

[ 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.
  • %All Users Profile%\Application Data\Microsoft\Windows\{Malware Name}.exe
  • %All Users Profile%\Desktop\DECRYPT_INSTRUCTION.html
  • %Desktop%\DECRYPT_INSTRUCTION.html

Step 6

Search and delete these folders

[ Learn More ]
Please make sure you check the Search Hidden Files and Folders checkbox in the More advanced options option to include all hidden folders in the search result.
  • %All Users Profile%\Application Data\Microsoft\Windows

Step 7

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