A new phishing campaign taking advantage of an easily exploitable issue in Microsoft Teams to deliver malware has been flagged by researchers.

Late last month, Truesec researchers spotted two compromised Microsoft 365 accounts sending HR-themed messages with a malicious attachment to enterprise targets.

Zip – is downloaded from a SharePoint site and, once opened, it eventually leads to the execution of an AutoIT script that launches shellcode to load the DarkGate loader Windows executable.

As noted earlier, Jumpsec researchers have recently uncovered a bug in Microsoft Teams that could allow threat actors to deliver malware into employees’ inboxes, by bypassing client-side security controls that disallow external tenants to send files to employees.

“Unfortunately, current Microsoft Teams security features such as Safe Attachments or Safe Links was not able to detect or block this attack,” Jakob Nordenlund, senior cyber security consultant at Truesec concluded.

“Right now, the only way to prevent this attack vector within Microsoft Teams is to only allow Microsoft Teams chat requests from specific external domains, albeit it might have business implications since all trusted external domains need to be whitelisted by an IT administrator.”