A new campaign is targeting people with messages that
seem to come from the U.S. Department of Labor (DoL), trying to trick them into
opening a DOC file, enabling macros, and eventually deploying the TrickBot
malware.
Like many of today’s malicious campaigns, this new one
tries to use COVID-19 as a cover to give it a sense of urgency. The use of an
official government institution is a well-known tactic and, in this case, the
bad actors impersonate the Department of Labor.
The email message talks about a provision called the
Family and Medical Leave Act (FMLA), which allows sick employees to receive
benefits when they miss work. Given the economic situation, the email aims to
convince people that they need to read a document attached to the email.
An analysis from IBM
X-Force of the email shows that it contains one malicious file,
named “Family and Medical Leave of Act 22.04.doc.” It’s an actual DOC file but
asks for the users to enable Macros when opened. When the file is closed, the
attack runs scripts.
Macros are very useful in office suites, used to display
dynamic content or for various automatization procedures, but they should
remain off at all times. They can be used to execute scripts, allowing
attackers to download malware.
And this is precisely the route taken in this case. After
the user enables Macros, a file named terop.bat is downloaded and executed. But
things get iffy from there, as the attackers use cURL to download a number of
files from a compromised domain, only to fail. cURL is not available by default
in Windows-powered machines, so the commands present in the .bat file fail.
The researchers presume the attackers are still testing deployment
methods and procedures, and that’s why the download fails. But looking at the
IP address and the type “Macros on close” method indicates that the malware to
be eventually downloaded is Trickbot.
The Trickbot malware is adaptive and is used with
different attack vectors. It initially started as a credential-harvesting
threat, mostly focusing on e-banking, but it has a modular structure and allows
the use of specialized plugins that lets bad actors change its purpose
depending on the campaign.
Users are advised to never open emails from unknown
contacts and to be wary of any messages from seemingly official organizations
and institutions. Also, remember to keep Macros turned off at all times.