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WORM_WCRY.B

May 16, 2017
 Analysis by: Byron Jon Gelera
 ALIASES:

Ransom.Wannacry (Symantec); Trojan.Ransom.WannaCryptor.H (F-secure); W32/WannaCryptor.D!tr (Fortinet)

 PLATFORM:

Windows

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

  • Threat Type: Worm

  • Destructiveness: No

  • Encrypted:

  • In the wild: Yes

  OVERVIEW


This Worm 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:

3,723,264 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

15 May 2017

Arrival Details

This Worm 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 Worm drops and executes the following files:

  • %Windows%\tasksche.exe → detected as Ransom_WCRY.SMB

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

Autostart Technique

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

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
services\mssecsvc2.0
DisplayName = Microsoft Security Center (2.0) Service

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
services\mssecsvc2.0
ImagePath = {initial malware file path} -m security

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
services\mssecsvc2.0
ObjectName = LocalSystem

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
services\mssecsvc2.0
ErrorControl = "1"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
services\mssecsvc2.0
Start = "2"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
services\mssecsvc2.0
Type = "16"

It registers as a system service to ensure its automatic execution at every system startup by adding the following registry keys:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
services\mssecsvc2.0

It starts the following services:

  • mssecsvc2.0

Other Details

This Worm connects to the following possibly malicious URL:

  • randomly-generated IP address over the Internet

It does the following:

  • It connects to http://www.iuqerfsodp9ifjaposdfjhgosurijfaewrwergwea.com. If the connection is successful, it will stop execution. Hence, it is used as a kill switch for the infection.

  SOLUTION

Minimum Scan Engine:

9.850

FIRST VSAPI PATTERN FILE:

13.406.08

FIRST VSAPI PATTERN DATE:

14 May 2017

VSAPI OPR PATTERN File:

13.407.00

VSAPI OPR PATTERN Date:

15 May 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

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.

 
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\services
    • mssecsvc2.0

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.
  • %WINDOWS%\tasksche.exe

Step 6

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


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