A new variant of the infamous Agent Tesla spyware was spotted by experts at Fortinet, the malware has been spreading via weaponize Microsoft Word documents.

Agent Tesla is a spyware that is used to spy on the victims by collecting keystrokes, system clipboard, screenshots, and credentials from the infected system. To do this, the spyware creates different threads and timer functions in the main function.

The experts first discovered the malware in June, when they observed threat actors spreading it via a Microsoft Word document containing an auto-executable malicious VBA Macro.

Once the users have enables the macro, the spyware will be installed on the victim’s machine

The mail used in the last campaign contains text that appears not clear and it asks users to double click to enable the clear view.

Agent Tesla

“As you can see, it asks the victim to double click the blue icon to enable a “clear view.” Once clicked, it extracts an exe file from the embedded object into the system’s temporary folder and runs it.  In this case, the exe file is called “POM.exe”.” continues the blog post.

When the users click on the blue icon, a POM.exe file written in Visual Basic being extracted from the embedded object, then it is saved to the system’s temporary folder and executed.

According to Fortinet, the POM.exe is a sort of installer for the final malware.

“Based on my analysis, it’s a kind of installer program. When it runs, it drops two files: “filename.exe” and “filename.vbs” into the “%temp%subfolder”. It then exits the process after executing the file “filename.vbs”.  Below, in figure 4, is the content of “filename.vbs”.” continues the analysis.

The variant used in the last campaign is similar to the older one except for the usage of the SMTPS to send the collected data to the attacker’s email box, instead of HTTP POST requests.

“However, the way of submitting data to the C&C server has changed. It used to use HTTP POST to send the collected data. In this variant, it uses SMTPS to send the collected data to the attacker’s email box.” continues the analysis.

“Based on my analysis, the commands used in the SMTP method include “Passwords Recovered”, “Screen Capture”, and “Keystrokes”, etc.  The commands are identified within the email’s “Subject” field.  For example:

“System user name/computer name Screen Capture From: victim’s IP”

The attackers used a free Zoho email account for this campaign.

Further details

Pierluigi Paganini

(Security Affairs – Agent Tesla, spyware)

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