Threat Actors Deliver Courier-Themed Spam Campaign with Attached ACE Files

Insights and Analysis by Miguel Ang

Trend Micro researchers detected a new courier service themed malicious spam campaign that uses ACE files (detected by Trend Micro as Trojan.Win32.GULOADER.A) as attachments. The samples were gathered from our honeypot.

Figure 1. Sample DHL-themed spam email

The ACE file contains a zip file and an executable payload, which acts as a downloader upon extraction and execution.

Figure 2. Attachment Contents

The zip is password protected and contains another executable.

Figure 3. DHL themed spam

The binary is a downloader that will access a link to download its payload, set up a startup registry, and execute the payload using a VBS script. The indicated link does not download a file. However, the setup still makes future compromise possible.

Figure 4. Binary file from the malicious attachment

We have been receiving other spam samples with the same payload. ACE is a data compression archive produced by WinACE. It can be opened using tools such as WinACE or BitZipper.

Delivery services themed campaigns are not new; earlier campaigns we detected delivered backdoor, Emotet, trojans, and other malware types. Other payloads made it possible to intercept text messages.

 
Thwarting spam campaigns

• Do not download attachments or click links from unverified sources.
• If the email comes from a seemingly familiar source, verify via the company’s phone number or other contact details if they indeed sent the email.
• If the company sent legitimate emails before, check the new sender’s email address. If it is an entirely different source or the email address is spoofed, the email is most likely spam.
• Take advantage of security solutions for spam and other email-based threats such as phishing and business email compromise (BEC).

Indicators of Compromise