Threat Explorer

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29 March 2016
06 July 2017
Also Known As:
Trojan.Cryptolocker.AJ [Symantec]
Infection Length:
Systems Affected:
Ransom.Petya is a Trojan horse that encrypts files on the compromised computer.

Note: Definitions prior to August, 2016 may detect this threat as Trojan.Cryptolocker.AJ

For more information, please see the following resource:
Petya ransomware outbreak: Here’s what you need to know

Antivirus Protection Dates

  • Initial Rapid Release version 20 May 2016 revision 034
  • Latest Rapid Release version 03 August 2019 revision 019
  • Initial Daily Certified version 20 May 2016 revision 049
  • Latest Daily Certified version 04 August 2019 revision 002
  • Initial Weekly Certified release date 30 March 2016
Click here for a more detailed description of Rapid Release and Daily Certified virus definitions.
Note: This Trojan has two variants, listed here as Original variant and June 2017 variant .

June 2017 variant:
The Trojan propagates on the local network via a Windows exploit. It may also spread via a Trojanized MeDoc update.

Once executed, the Trojan creates the following files:
  • C:\Windows\perfc : Infection marker
  • C:\Windows\perfc.dat : The Trojan
  • %Windir%\dllhost.dat : Legitimate copy of PsExec
  • %AppData%\dllhost.dat : Legitimate copy of PsExec
  • %SystemDrive%\README.TXT : Ransom note
  • %Temp%\[RANDOM].tmp

The Trojan adds the following scheduled task in order to restart the computer:
  • %Windir%\system32\shutdown.exe /r /f

The Trojan will try to spread itself similar to a worm. First it will discover other computers to infect using the following methods:
  • All IP addresses and DHCP servers of all network adaptors
  • All DHCP clients of the DHCP server if ports 445/139 are open
  • All IP addresses within the subnet as defined by the subnet mask if ports 445/139 are open
  • All computers you have a current open network connection with
  • All computers in the ARP cache
  • All resources in Active Directory
  • All server and workstation resources in Network Neighborhood
  • All resources in the Windows Credential Manager (including Remote Desktop Terminal Services computers)

In pursuit of the goal to spread, it will dump credentials from memory using a LSA dump tool. It attempts to use these credentials with PsExec or the Windows Management Instrumentation Command-line (WMIC) tool to infect remote computers. It will also try SMB remote exploits EternalBlue and EternalRomance.

The threat checks for certain process names corresponding to security products, and it will alter its behavior if certain ones are found. If Norton or SEP is found, the threat will not try to exploit EternalBlue/EternalRomance.

If the infection marker (usually C:\Windows\perfc, but this can change based on the original file name of the threat) is already present then the computer will not be encrypted.

The threat will overwrite the computer's MBR and after restarting will show a fake CHKDSK screen.

The Trojan encrypts files on the compromised computer with the following extensions:
  • .3ds
  • .7z
  • .accdb
  • .ai
  • .asp
  • .aspx
  • .avhd
  • .back
  • .bak
  • .c
  • .cfg
  • .conf
  • .cpp
  • .cs
  • .ctl
  • .dbf
  • .disk
  • .djvu
  • .doc
  • .docx
  • .dwg
  • .eml
  • .fdb
  • .gz
  • .h
  • .hdd
  • .kdbx
  • .mail
  • .mdb
  • .msg
  • .nrg
  • .ora
  • .ost
  • .ova
  • .ovf
  • .pdf
  • .php
  • .pmf
  • .ppt
  • .pptx
  • .pst
  • .pvi
  • .py
  • .pyc
  • .rar
  • .rtf
  • .sln
  • .sql
  • .tar
  • .vbox
  • .vbs
  • .vcb
  • .vdi
  • .vfd
  • .vmc
  • .vmdk
  • .vmsd
  • .vmx
  • .vsdx
  • .vsv
  • .work
  • .xls
  • .xlsx
  • .xvd
  • .zip

After encryption, the Trojan clears the following logs using wevtutil:
  • Setup
  • System
  • Security
  • Application

The Trojan deletes the USN journal using fsutil.

When the compromised computer is restarted, the Trojan displays a ransom note demanding payment in order for the files to be decrypted.

The Trojan demands a payment of $300 in bitcoin to 1Mz7153HMuxXTuR2R1t78mGSdzaAtNbBWX and tells the user to email to get the decryption key. However the email account has been shut down by the provider and decryption of the files is not currently possible.

The Trojan will run every time the computer starts.

Original variant:
The Trojan may be spread through emails containing download links for the malware.

The Trojan overwrites and encrypts the master boot record (MBR) and the first sectors of the principal disk on the compromised computer.

The Trojan then forces the computer to restart.

The Trojan mimics the CHKDSK utility while it modifies the MBR.

The Trojan then restarts the compromised computer again and displays an ASCII image of a skull and crossbones with a prompt for the user to press any key.

When the user presses a key, the Trojan displays a ransom note demanding payment in order for the files to be decrypted.


Symantec Security Response encourages all users and administrators to adhere to the following basic security "best practices":

  • Use a firewall to block all incoming connections from the Internet to services that should not be publicly available. By default, you should deny all incoming connections and only allow services you explicitly want to offer to the outside world.
  • Enforce a password policy. Complex passwords make it difficult to crack password files on compromised computers. This helps to prevent or limit damage when a computer is compromised.
  • Ensure that programs and users of the computer use the lowest level of privileges necessary to complete a task. When prompted for a root or UAC password, ensure that the program asking for administration-level access is a legitimate application.
  • Disable AutoPlay to prevent the automatic launching of executable files on network and removable drives, and disconnect the drives when not required. If write access is not required, enable read-only mode if the option is available.
  • Turn off file sharing if not needed. If file sharing is required, use ACLs and password protection to limit access. Disable anonymous access to shared folders. Grant access only to user accounts with strong passwords to folders that must be shared.
  • Turn off and remove unnecessary services. By default, many operating systems install auxiliary services that are not critical. These services are avenues of attack. If they are removed, threats have less avenues of attack.
  • If a threat exploits one or more network services, disable, or block access to, those services until a patch is applied.
  • Always keep your patch levels up-to-date, especially on computers that host public services and are accessible through the firewall, such as HTTP, FTP, mail, and DNS services.
  • Configure your email server to block or remove email that contains file attachments that are commonly used to spread threats, such as .vbs, .bat, .exe, .pif and .scr files.
  • Isolate compromised computers quickly to prevent threats from spreading further. Perform a forensic analysis and restore the computers using trusted media.
  • Train employees not to open attachments unless they are expecting them. Also, do not execute software that is downloaded from the Internet unless it has been scanned for viruses. Simply visiting a compromised Web site can cause infection if certain browser vulnerabilities are not patched.
  • If Bluetooth is not required for mobile devices, it should be turned off. If you require its use, ensure that the device's visibility is set to "Hidden" so that it cannot be scanned by other Bluetooth devices. If device pairing must be used, ensure that all devices are set to "Unauthorized", requiring authorization for each connection request. Do not accept applications that are unsigned or sent from unknown sources.
  • For further information on the terms used in this document, please refer to the Security Response glossary.
You may have arrived at this page either because you have been alerted by your Symantec product about this risk, or you are concerned that your computer has been affected by this risk.

Before proceeding further we recommend that you run a full system scan . If that does not resolve the problem you can try one of the options available below.

If you are a Norton product user, we recommend you try the following resources to remove this risk.

Removal Tool

If you have an infected Windows system file, you may need to replace it using the Windows installation CD .

How to reduce the risk of infection
The following resources provide further information and best practices to help reduce the risk of infection.

If you are a Symantec business product user, we recommend you try the following resources to remove this risk.

Identifying and submitting suspect files
Submitting suspicious files to Symantec allows us to ensure that our protection capabilities keep up with the ever-changing threat landscape. Submitted files are analyzed by Symantec Security Response and, where necessary, updated definitions are immediately distributed through LiveUpdate™ to all Symantec end points. This ensures that other computers nearby are protected from attack. The following resources may help in identifying suspicious files for submission to Symantec.

Removal Tool

If you have an infected Windows system file, you may need to replace it using the Windows installation CD .

How to reduce the risk of infection
The following resource provides further information and best practices to help reduce the risk of infection.
Protecting your business network

The following instructions pertain to all current Symantec antivirus products.

1. Performing a full system scan
How to run a full system scan using your Symantec product

2. Restoring settings in the registry
Many risks make modifications to the registry, which could impact the functionality or performance of the compromised computer. While many of these modifications can be restored through various Windows components, it may be necessary to edit the registry. See in the Technical Details of this writeup for information about which registry keys were created or modified. Delete registry subkeys and entries created by the risk and return all modified registry entries to their previous values.
Writeup By: Hector Navarro Martin