While FortiGuard Labs was preparing for another presentation on our Locky research at the Black Alps cyber security conference this coming November in Switzerland, Fortinet’s Kadena Threat Intelligence System (KTIS)1 caught another Locky variant using a new extension – “ykcol” or “locky” spelled backwards.
Locky has been stepping up its game over the past few months after going dark during the first half of 2017. Just like the old days, this new variant is distributed through massive volumes of malicious spam email campaigns, which are usually named after the extension the variant uses for encryption. In this case, it uses “ykcol”.
Fig 1. Encrypted files with ‘.ykcol’ extension
Multiple Spam Waves
With the data collected from KTIS, we identified multiple spam waves of this new variant over the past three days. In fact, as we are writing this article new waves are still being discovered in our system which have similar behavior to previous spam waves. The table below shows a comparison between these waves.
Table 1. Comparison of the spam waves
The following generalizations can be made based on this data:
- Emails in the same wave have the same email subject and attachment filename format. (Except for the 5th wave, that had two sets of email subjecst and attachments)
- Each wave has its own set of different compromised hosts appended with the same URI. (see IOC for full list of related URLs)
- At the same point in time, compromised URLs in the same wave lead to the same locky sample when downloaded.
- A wave can deliver Locky samples with either online or offline encryption. Locky samples coming from the same wave that are capable of online encryption use the same C&C servers.
- All Locky samples analyzed in this campaign were distributed with an affiliate ID: 3. This affiliate has been observed distributing Locky through spam emails containing an attached compressed JS or VBS downloader since last year.
- Two spam waves were delivered per day.
Another interesting observation is about the email subject “Message from km_c224e” from the second wave. This same subject was also used in other malware campaigns delivering Dridex and Jaff Ransomware, which implies that one group may be responsible for these distributions.
As always, in an attempt to evade traditional signature detections, threat actors behind Locky repack and rehash the samples regularly.
Fig 2. Malicious URL leads to different “.ykcol” samples
Feedback from our Fortinet systems show that United States is the top affected country. This data only reflects the number of visits to Locky’s C&C’s, which means that the variants with offline decryption were not included in these statistics.
Fig 3. Top countries affected by Locky with online encryption
Aside from the filename extension change, Locky aligned the price for decryption with the increasing price of bitcoin. From the previous ransom of 0.5 BTC, they are now asking for 0.25BTC or ~1000USD.
Fig 4. Locky decryptor priced at 0.25BTC
Here is the updated list of all Locky extensions seen so far.
Table 2. List of Locky extensions
- FortiMail blocks all spam emails.
- FortiGuard Antivirus service detects Locky(.ykcol) samples as W32/Locky.FWSD!tr.ransom.
- FortiGuard Webfilter service blocks and tags all download URLs as malicious.
- FortiSandbox rates the Locky samples as High Risk
Despite a few minor alterations, Locky is still the same dangerous ransom malware from a year ago. It has the capabilities and distribution network necessary to cause significant damage to any system unfortunate enough to be hit by it.
Over the past few months, we have seen it distributing massive spam campaigns and we don’t see it slowing down any time soon.
-= FortiGuard Lion Team =-
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URL Download of Locky:
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 Fortinet's Kadena Threat Intelligence System (KTIS) is an interactive platform that extracts contextual information from files, URLs, and other artefacts for more accurate malware identification, fast-tracked analysis, detailed analytics, and easier data correlation.
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