022. That's How FIN7 Uses Malicious JAR Files

Hello everyone! Yesterday we talked about malicious JAR files. And guess what? I just ran into a fresh report from Sophos MDR team - they show how notorious FIN7 uses such files.

Let's start from how these files were delivered to the compromised system - it's also very interesting. First, the adversary sent a large volume of spam messages (over 3000). Shortly after the victim received a Teams call. The threat actor impersonated a help desk specialist and asked to allow a remote screen control session through Teams. Using this session to drop malicious files to the compromised system.

And yes, the first stage is a JAR file, which was executed through the same remote session:

C:\Users\Public\Documents\MailQueue-Handler\jdk-23.0.1\bin\javaw.exe -jar C:\Users\Public\Documents\MailQueue-Handler\MailQueue-Handler.jar

Another malicious JAR file leveraged by the threat actors is a credential harvester:

“C:\Users\Public\Documents\MailQueue-Handler\jdk-23.0.1\bin\javaw.exe” -jar C:\Users\Public\Documents\MailQueue-Handler\identity.jar

Similar email bombing case was covered by Rapid7 in December 2024. The adversary also used a malicous JAR file named identity.jar:


As you can see, JAR files are not that rare, so it's a good candidate for your threat hunting missions!

See you tomorrow!

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