It's that time of year where the seasons are changing. The Northern Hemisphere moves into Autumn, and the Southern Hemisphere moves to Spring. So it is with Locky. As we discussed in our last post, spam campaigns were downloading Locky ransomware that used ".lukitus" as the encrypted file extension name. Now Necurs botnet is back spamming out Locky again, only this time with a different file extension name.
Our Spam Research Database shows the spikes of emails coming from the Necurs botnet on Sept 19, 2017.
The table below shows the top 10 countries where Necurs spam originates from. These numbers indicate machines compromised with Necurs
Samples of the email messages are shown below. They come with two different subject lines:
These messages come with .7zip attachments that contains .vbs files:
Examining the .vbs code closely, you can find the URLs that are accessed once the .vbs file is executed. The image below shows a code snippet of the URLs
Accessing these URLs, can download the Locky ransomware executable files:
Below are images for URL requests and responses respectively:
Downloaded executable files(metadata):
SIZE: 649,216 bytes
After the .vbs script finishes downloading the executable file, it will automatically execute the ransomware, which, as expected, it encrypts your files. Note that the file extension has been changed to ".ykcol" which is Locky spelled backwards:
List of file extensions that this variant will encrypt:
Locky ransom notes in various formats:
Image File (ykcol.bmp):
HTML File (ykcol.htm)
Added Registry to change wallpaper into the ransom note.
Finally, the image below shows the Locky decryptor site. The victim needs to use a TOR browser to access the URL provided in the ransom note:
Asking for 0.25 BTC or USD 1000
Indicators of Compromise (IoCs)