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ASEC Weekly Malware Statistics (August 29th, 2022 – September 4th, 2022)

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The ASEC analysis team is using the ASEC automatic analysis system RAPIT to categorize and respond to known malware. This post will list weekly statistics collected from August 29th, 2022 (Monday) to September 4th, 2022 (Sunday).

For the main category, info-stealer ranked top with 45.9%, followed by downloader with 28.1%, backdoor with 18.5%, ransomware with 6.2%, and CoinMiner and banking malware with 0.7% each.

Top 1 – GuLoader

GuLoader, which ranked first place with 22.6%, is a downloader malware that downloads additional malware and runs it. It was packed with Visual Basic language in the past to bypass detection, but it is now distributed in a form of an NSIS installer. It used to be known as CloudEye but got the name GuLoader because Google Drive is frequently used as a download URL. In addition to Google Drive, various URLs such as One Drive from Microsoft and Discord can also be used.

Instead of being downloaded in a file form, GuLoader is downloaded on memory to avoid detection, and the downloaded file is encoded, not PE. It is then executed after being decoded in the memory, downloading malware such as infostealer (Formbook and AgentTesla) and RAT (Remcos and NanoCore).

As most are distributed through spam emails disguised as invoices, shipment documents, and purchase orders, the file names contain such words shown above (Invoice, Shipment, and P.O. – Purchase Order). Some samples have extensions disguised as document files such as pdf and xlsx or Auto CAD blueprint files such as dwg.

Top 2 – Agent Tesla

AgentTesla is an infostealer that ranked second place with 17.8%. It is an info-stealer that leaks user credentials saved in web browsers, emails, and FTP clients.

How AgentTesla Malware is Being Distributed in Korea

It uses e-mail to leak collected information, and there are samples that used FTP or Discord API. C&C information of recently collected samples is as follows.

As most are distributed through spam emails disguised as invoices, shipment documents, and purchase orders, the file names contain such words shown above (Invoice, Shipment, and P.O. – Purchase Order). Multiple collected samples were disguised as files with extensions of pdf and xlsx.

Top 3 – Formbook

Formbook ranked third place with 13.0%.

Like other info-stealer, it is mainly distributed through spam emails. The distributed file names are close to each other.

As Formbook is injected into normal processes (one is a running explorer.exe and the other is in system32), the malicious behaviors are performed by these normal processes. Besides user credentials in the web browser, the malware can steal various information through keylogging, clipboard grabbing, and web browser form grabbing.

Below is the list of confirmed C&C server URLs of Formbook.

Top 4 –  Lokibot

Lokibot malware ranked fourth place with 12.3%. It is an info-stealer that leaks information about programs such as web browsers, email clients, and FTP clients.

The following is a list of the most C&C servers for the malware.

Top 5 –  Remcos

This week, Remcos ranked fifth place with 6.2%. Remcos is a RAT malware that carries out various commands given by the attacker such as keylogging and information leaking.

Remcos RAT Malware being Distributed as Spam Mail
Remcos is packed with a .NET packer and is distributed as attachments to spam emails, just like AgentTesla, Formbook, and NanoCore. Recently, there are some cases where it got distributed after disguising itself as a certain tool.
The confirmed C&C server URLs of Remcos are as follows.

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