Analysis by: Anthony Joe Melgarejo


Win32/Exploit.CVE-2017-0147.A (ESET-NOD32), Ransom:Win32/WannaCrypt (Microsoft), Ransom.Wannacry (Symantec)




  • Threat Type: Worm

  • Destructiveness: No

  • Encrypted: No

  • In the wild: Yes


Infection Channel: Propagates via network shares

This Worm executes the dropped file(s). As a result, malicious routines of the dropped files are exhibited on the affected system.


File Size: 3723264 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 12 May 2017
Payload: Drops files

Arrival Details

This malware arrives via the following means:

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:

Type = "16"

Start = "2"

ErrorControl = "1"

ImagePath = {initial malware file path} -m security

DisplayName = Microsoft Security Center (2.0) Service

ObjectName = LocalSystem

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


It starts the following services:

  • mssecsvc2.0

Dropping Routine

This Worm drops the following files:

It executes the dropped file. As a result, malicious routines of the dropped file are exhibited on the affected system.


It connects to If the connection is successful, it will stop execution. Hence, it is used as a kill switch for the infection.

It scans the following to check for open port 445:

  • Hosts on the Local Area Network
  • randomly-generated IP address over the Internet

If it finds a host either on the LAN/Internet with open port 445, it will attempt to exploit MS17-010 vulnerability to drop and execute a copy of itself to the remote host.

It uses the following file path for its dropped copies on the remote hosts:

  • %Windows%\mssecsvc.exe

It checks for the presence of the file %WINDOWS%\tasksche.exe. If the file exist, it will move the file to the following directory %WINDOWS%\qeriuwjhrf\tasksche.exe.

It executes %Windows%\tasksche.exe with /i parameter.


Minimum Scan Engine: 9.850

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

Remove the malware/grayware file dropped/downloaded by WORM_WCRY.A. (Note: Please skip this step if the threat(s) listed below have already been removed.)

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. Before you could do this, you must restart in Safe Mode. For instructions on how to do this, you may refer to this page If the preceding step requires you to restart in safe mode, you may proceed to edit the system registry.

  • In HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\services
    • mssecsvc2.0

Step 5

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