Malicious spam campaigns delivering banking Trojans

[harlan4096]

In mid-March 2021, we observed two new spam campaigns. The messages in both cases were written in English and contained ZIP attachments or links to ZIP files. Further research revealed that both campaigns ultimately aimed to distribute banking Trojans. The payload in most cases was IcedID (Trojan-Banker.Win32.IcedID), but we have also seen a few QBot (Backdoor.Win32.Qbot, also known as QakBot) samples. During campaign spikes we observed increased activity of these Trojans: more than a hundred detections a day.

IcedID is a banking Trojan capable of web injects, VM detection and other malicious actions. It consists of two parts – the downloader and the main body that performs all the malicious activity. The main body is hidden in a PNG image, which is downloaded and decrypted by the downloader.

QBot is also a banking Trojan. It’s a single executable with an embedded DLL (main body) capable of downloading and running additional modules that perform malicious activity: web injects, email collection, password grabbing, etc.

Neither of these malware families are new – we’ve seen them being distributed before via spam campaigns and different downloaders, like the recently taken-down Emotet. However, in the recent campaign we observed several changes to the IcedID Trojan.

Technical detailsInitial infectionDotDat

The first campaign we called ‘DotDat’. It distributed ZIP attachments that claimed to be some sort of cancelled operation or compensation claims with the names in the following format [document type (optional)]-[some digits]-[date in MMDDYYYY format]. We assume the dates correspond with the campaign spikes. The ZIP archives contained a malicious MS Excel file with the same name.

The Excel file downloads a malicious payload via a macro (see details below) from a URL with the following format [host]/[digits].[digits].dat and executes it.

The URL is generated during execution using the Excel function NOW(). The payload is either the IcedID downloader (Trojan.Win32.Ligooc) or QBot packed with a polymorph packer.

Excel macro details (3e12880c20c41085ea5e249f8eb85ded)

The Excel file contains obfuscated Excel 4.0 macro formulas to download and execute the payload (IcedID or QBot). The macro generates a payload URL and calls the WinAPI function URLDownloadToFile to download the payload.

After a successful download, the payload is launched using the EXEC function and Windows Rundll32 executable.The spam emails of the second campaign contained links to hacked websites with malicious archives named “documents.zip”, “document-XX.zip”, “doc-XX.zip” where XX stands for two random digits.

Like in the first campaign, the archives contained an Excel file with a macro that downloaded the IcedID downloader. According to our data, this spam campaign peaked on 17/03/2021. By April, the malicious activity had faded away.

Excel macro details (c11bad6137c9205d8656714d362cc8e4)

Like in the other case, Excel 4.0 macro formulas and the URLDownloadToFile function are used in this campaign. The main difference in the download component is that the URL is stored in a cell inside the malicious file.

Though the URL seems to refer to a file named “summer.gif”, the payload is an executable, not a GIF image. To execute the payload, the macro uses WMI and regsvr32 tools.

IcedID

As we mention above, IcedID consists of two parts – downloader and main body. The downloader sends some user information (username, MAC address, Windows version, etc.) to the C&C and receives the main body. In the past, the main body was distributed as a shellcode hidden in a PNG image. The downloader gets the image, decrypts the main body in the memory and executes it. The main body maps itself into the memory and starts to perform its malicious actions such as web injects, data exfiltration to the C&C, download and execution of additional payloads, exfiltration of system information and more.

IcedID new downloader

Besides the increase in infection attempts, the IcedID authors also changed the downloader a bit. In previous versions it was compiled as an x86 executable and the malware configuration after decryption contained fake C&C addresses. We assume this was done to complicate analysis of the samples. In the new version, the threat actors moved from x86 to an x86-64 version and removed the fake C&Cs from the configuration.
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