A  new ransomware has been discovered called Locky that encrypts your data using AES encryption and then demands .5 bitcoins to decrypt your files.  Though the ransomware sounds like one named by my kids, there is nothing childish about it.  It targets a large amount of file extensions and even more importantly, encrypts data on unmapped network shares.  Encrypting data on unmapped network shares is trivial to code and the fact that we saw the recent DMA Locker with this feature and now in Locky, it is safe to say that it is going to become the norm.  Like CryptoWall, Locky also completely changes the filenames for encrypted files to make it more difficult to restore the right data.  

At this time, there is no known way to decrypt files encrypted by Locky. For those who wish to discuss this ransomware or have questions, please feel free to post in our .

Locky installed via fake invoices

Locky is currently being distributed via email that contains Word document attachments with malicious macros. The email message will contain a subject similar to ATTN: Invoice J-98223146 and a message such as "Please see the attached invoice (Microsoft Word Document) and remit payment according to the terms listed at the bottom of the invoice".  An example of one of these emails can be seen below.

Locky Email Distribution
Locky Email Distribution

Attached to these email messages will be a malicious Word document that contains a name similar to invoice_J-17105013.doc. When the document is opened, the text will be scrambled and the document will display a message stating that you should enable the macros if the text is unreadable.

Malicious Word Document
Malicious Word Document

Once a victim enables the macros, the macros will download an executable from a remote server and execute it.

Malicious Macro
Malicious Macro

The file that is downloaded by the macro will be stored in the %Temp% folder and executed. This executable is the Locky ransomware that when started will begin to encrypt the files on your computer.

Locky encrypts your data and completely changes the filenames

When Locky is started it will create and assign a unique 16 hexadecimal number to the victim and will look like F67091F1D24A922B. Locky will then scan all local drives and unmapped network shares for data files to encrypt. When encrypting files it will use the AES encryption algorithm and only encrypt those files that match the following extensions:

.mid, .wma, .flv, .mkv, .mov, .avi, .asf, .mpeg, .vob, .mpg, .wmv, .fla, .swf, .wav, .qcow2, .vdi, .vmdk, .vmx, .gpg, .aes, .ARC, .PAQ, .tar.bz2, .tbk, .bak, .tar, .tgz, .rar, .zip, .djv, .djvu, .svg, .bmp, .png, .gif, .raw, .cgm, .jpeg, .jpg, .tif, .tiff, .NEF, .psd, .cmd, .bat, .class, .jar, .java, .asp, .brd, .sch, .dch, .dip, .vbs, .asm, .pas, .cpp, .php, .ldf, .mdf, .ibd, .MYI, .MYD, .frm, .odb, .dbf, .mdb, .sql, .SQLITEDB, .SQLITE3, .asc, .lay6, .lay, .ms11 (Security copy), .sldm, .sldx, .ppsm, .ppsx, .ppam, .docb, .mml, .sxm, .otg, .odg, .uop, .potx, .potm, .pptx, .pptm, .std, .sxd, .pot, .pps, .sti, .sxi, .otp, .odp, .wks, .xltx, .xltm, .xlsx, .xlsm, .xlsb, .slk, .xlw, .xlt, .xlm, .xlc, .dif, .stc, .sxc, .ots, .ods, .hwp, .dotm, .dotx, .docm, .docx, .DOT, .max, .xml, .txt, .CSV, .uot, .RTF, .pdf, .XLS, .PPT, .stw, .sxw, .ott, .odt, .DOC, .pem, .csr, .crt, .key, wallet.dat

Furthermore, Locky will skip any files where the full pathname and filename contain one of the following strings:

tmp, winnt, Application Data, AppData, Program Files (x86), Program Files, temp, thumbs.db, $Recycle.Bin, System Volume Information, Boot, Windows

When Locky encrypts a file it will rename the file to the format [unique_id][identifier].locky.  So when test.jpg is encrypted it would be renamed to something like F67091F1D24A922B1A7FC27E19A9D9BC.locky.  The unique ID and other information will also be embedded into the end of the encrypted file.

It is important to stress that Locky will encrypt files on network shares even when they are not mapped to a local drive. As predicted, this is becoming more and more common and all system administrators should lock down all open network shared to the lowest permissions possible.

As part of the encryption process, Locky will also delete all of the Shadow Volume Copies on the machine so that they cannot be used to restore the victim's files. Locky does this by executing the following command:

vssadmin.exe Delete Shadows /All /Quiet

In the Windows desktop and in each folder where a file was encrypted, Locky will create ransom notes called _Locky_recover_instructions.txt. This ransom note contains information about what happened to the victim's files and links to the decrypter page.

Locky Text Ransom Note
Locky Text Ransom Note

Locky will change the Windows wallpaper to %UserpProfile%\Desktop\_Locky_recover_instructions.bmp, which contains the same instructions as the text ransom notes.

Locky Wallpaper
Locky Wallpaper

Last, but not least, Locky will store various information in the registry under the following keys:

  • HKCU\Software\Locky\id - The unique ID assigned to the victim.
  • HKCU\Software\Locky\pubkey - The RSA public key.
  • HKCU\Software\Locky\paytext - The text that is stored in the ransom notes.
  • HKCU\Software\Locky\completed    - Whether the ransomware finished encrypting the compute.r

 

The Locky Decrypter Page

Inside the Locky ransom notes are links to a Tor site called the Locky Decrypter Page. This page is located at 6dtxgqam4crv6rr6.onion and contains the amount of bitcoins to send as a payment, how to purchase the bitcoins, and the bitcoin address you should send payment to.  Once a victim sends payment to the assigned bitcoin address, this page will provide a decrypter that can be used to decrypt their files.

Locky Decrypter Page
Locky Decrypter Page

 

Locky related Files

%UserpProfile%\Desktop\_Locky_recover_instructions.bmp
%UserpProfile%\Desktop\_Locky_recover_instructions.txt
%Temp%\[random].exe

Locky related Registry entries

HKCU\Software\Locky
HKCU\Software\Locky\id
HKCU\Software\Locky\pubkey	
HKCU\Software\Locky\paytext
HKCU\Software\Locky\completed	1
HKCU\Control Panel\Desktop\Wallpaper	"%UserProfile%\Desktop\_Locky_recover_instructions.bmp"