Resilient Ransomware: Locky Evades Detection through WSF Files

Resilient Ransomware: Locky Evades Detection through WSF Files

ransomware-sensorstechforumLocky ransomware is one of the crypto virus cases that hasn’t been solved so far and continues to evolve. No Locky decrypter is available for victims to unlock their files freely. New spam campaigns spreading Locky were just detected by TrendMicro researchers. This campaign, however, is different than previous operations, as it has adopted a new tactic – using Windows Scripting File for the arrival of the ransomware on the victim’s machine. The deployment of WSF is not something unseen, as it has already been done by another popular ransomware – Cerber. The Cerber’s campaign built on the WSF was detected in May this year, and it was quite successful.

Perhaps that’s the reason which drove Locky operators towards the inclusion of this tactic in their new campaigns.

Related: New Locky Spam Attacks! Beware of Necurs Malware

The success of WSF files is due to the fact that those files are not usually monitored for malicious activities by endpoint security solutions.

A Look into the Latest Locky Campaign Based on WSF Files

Like in previous campaigns, the ransomware is using spam emails with .ZIP files attachments. The attachments contain the WSF files.

The spam emails usually have subject lines like:

  • “bank account record”
  • “annual report”
  • “company database”

Because of the subject lines, researchers believe that the ransomware operators are targeting companies. Most of the spam emails were observed to be sent between 9 a.m. and 11 a.m. UTC. This is the time when business employees start work in most European countries. Moreover, the volume of spam was much higher during the weekdays and less during the weekends. This is a clear indication that the latest Locky campaign has chosen to attack companies.

The first wave of this spam campaign was seen on July 15—with each email originating from different IP addresses. The countries that sent out the initial spam run were Serbia, Colombia, and Vietnam. Then another wave of spam runs were seen on July 18 and 19, with emails coming from countries such as Thailand and Brazil.

Why Are Ransomware Operators Using WSF Files?

First Cerber, and now Locky operators are adopting WSF files. Like we already said, Windows Scripting Files allow the ransomware to bypass security measures like sandbox analysis and blacklisting. The WSF files play the role of downloaders of the ransomware. Furthermore, WSF files enable malicious operators to download whatever malware payload they want, like with using VBScript and JavaScript.

When downloaded files have different hashes, detecting them via blacklisting becomes difficult. The samples we analyzed have properties of a “Yahoo Widget” file to pass it off as legitimate.

A Registry Key Employed to Determine the System’s Language before Dropping Locky

Besides the employment of the WSF files, this campaign has been observed to also add a registry key to determine the system’s language. This is not the first time ransomware uses registry keys to do – the same behavior was previously seen in Jigsaw, CryptoLock and Reveton ransomware.

SSH Protocol Used for the Command and Control Communication

The latest Locky is also observed to use the SSH protocol or openVPN to encrypt the network traffic. Researchers report that one of the c&c servers is from the Deep Web via a specific Tor site – zjfq4lnfbs7pncr5[.]onion[.]to.
This threat also appends the .zepto file extension. Also, the ransomware uses native APIs to change the file extension.

All proof points to the fact that the operators of this campaign are from Brazil. Researchers were able to spot the latest Locky being sold in the Brazilian underground market, which is one of the most developed and well-organized markets.

Researchers also say that they found a Facebook user sharing a specific blog post:

We also found someone (with the aliasunknown_antisec) using Facebook to share this blog post (originally posted in Trend Micro blog in Brazil) that discussed our findings about the Brazilian underground. That particular user also included a caption in Brazilian Portuguese that can be translated to, “Sup dog, they’ve got you ransomware.”

It’s not the first time Brazilian cybercriminals use social media to advertise their products and services.

Latest Locky WSF Campaign: Removal, Prevention and Conclusion

Locky is definitely evolving – initially the threat used macros, then switched to JavaScript and VBScript and currently to WSF. “With this file type, it can, by default, combine any scripting language like JScript, which was previously used by RAA for obfuscation purposes“, researchers point out.

Since this variant is able to bypass traditional and sandbox analysis, it should be stopped at the exposure layer. TrendMicro says that they were able to protect their customers at the gateway level by detecting Locky-related spam emails.

If You Have Been Infected by Locky…

The very thing every victim should do is remove the ransomware from their system. The easiest way to do so is by using an anti-malware program.

Then, victims can try and restore some of their encrypted files via data recovery software, such as:

  • Stellar Phoenix Windows Data Recovery Software
  • In the future, continuously back up your data so that it never falls victim to crypto viruses.

    Spy Hunter scanner will only detect the threat. If you want the threat to be automatically removed, you need to purchase the full version of the anti-malware tool.Find Out More About SpyHunter Anti-Malware Tool / How to Uninstall SpyHunter

    Milena Dimitrova

    Milena Dimitrova

    An inspired writer and content manager who has been with SensorsTechForum since the beginning. Focused on user privacy and malware development, she strongly believes in a world where cybersecurity plays a central role. If common sense makes no sense, she will be there to take notes. Those notes may later turn into articles! Follow Milena @Milenyim

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