Pierluigi Paganini July 15, 2017

Security experts at the SANS Institute discovered that that NemucodAES ransomware and Kovter trojan are being delivered together in spam campaigns.

Security experts at the SANS Institute Internet Storm Center, discovered that that two malware families, NemucodAES and Kovter are being delivered together in .zip attachments delivered via active spam campaigns.

Security Researcher Brad Duncan noticed in the last couple of weeks a significant increase in malicious spam delivering .zip archives with JavaScript files used to download and execute the NemucodAES ransomware and Kovter click-fraud malware.

NemucodAES is a variant of the Nemucod Trojan downloader, known for being used in different campaigns in 2016 distributing Locky and TeslaCrypt ransomware.

“By March 2016, we started seeing reports of ‘Nemucod ransomware’ that stopped downloading ransomware binaries in favor of using its own script-based ransomware component,” Duncan wrote in a SANS Institute Internet Storm Center posted Friday.

“And now in July 2017, we see the next phase of Nemucod ransomware: NemucodAES.  Emisoft states this new variant is written in JavaScript and PHP.  It uses AES and RSA to encrypt a victim’s files.”

The NemucodAES ransomware is easy to neutralize due to the availability of a decryptor, meanwhile, Kovter click-fraud is a fileless malware hard to detect. Kovter was also used by threat actors to steal personal information and download and execute additional malicious payloads.

Spam campaigns deliver the malicious .zip archives disguised as notices from the United Parcel Service.

“Malspam with Zip archives containing JavaScript files are easy for most organizations to detect… But some of these messages might slip past your filtering, and some people could possibly get infected.  With the NemucodAES decryptor, people can recover their files, but I expect this ransomware will continue to evolve,” Duncan wrote.

Kovter was packaged with other ransomware in past campaigns, in February, experts at Microsoft’s Malware Protection Center spotted malicious email campaigns using .lnk attachments to spread Locky ransomware and Kovter.

Back to the recent campaign, NemucodAES and Kovter were bundled in malicious .zip archives. When victims unpack the archives a JavaScript file is extracted.

“Network traffic was typical for an infection by one of the .js files.  We first see HTTP requests for the NemucodAES JavaScript, followed by requests for various executables.  Then we see the post-infection Kovter traffic.  NemucodAES doesn’t generate any traffic on its own,” according to the research report.

The NemucodAES ransomware encrypt files without appending any info to the original file names, then it delivers in the “AppData\Local\Temp” directory instructions (via an .hta file) to decrypt the files. It also uses a Windows desktop background (a .bmp file) as the ransomware note.

Victims are requested to pay a $1,500 ransom in Bitcoin.

Experts are investigating the presence of the Kovter malware in the campaigns. Kovter seems to be used only to check traffic and generating command-and-control traffic.

“I see a lot of post-infection events for Kovter command and control traffic. But I’m not certain click-fraud is involved any more,” Duncan said. 

Give a look at the SANS’s analysis for further details about this campaign.

Pierluigi Paganini

(Security Affairs – NemucodAES ransomware, spam)

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