Pierluigi Paganini October 16, 2023

Researchers uncovered an ongoing campaign abusing popular messaging platforms Skype and Teams to distribute the DarkGate malware.

From July to September, researchers from Trend Micro observed a malicious campaign DarkGate campaign abusing instant messaging platforms to deliver a VBA loader script to victims.

The threat actors abused popular messaging platforms such as Skype and Teams to deliver a script used as a loader for a second-stage payload, which was an AutoIT script containing the DarkGate malware. The researchers speculate the originating accounts of the instant messaging applications were compromised through the leaked credentials available on cybercrime forums.

DarkGate is a commodity malware that was first spotted by Fortinet researchers in 2017, it supports multiple features, including the ability to perform the following operations:

• Execute discovery commands (including directory traversal)
• Self-update and self-manage
• Implement remote access software (such as remote desktop protocol or RDP, hidden virtual network computing or hVNC, and AnyDesk)
• Enable cryptocurrency mining functionality (start, stop, and configure)
• Perform keylogging
• Steal information from browsers
• Privilege escalation

In the latest campaign, threat actors abused a trusted relationship between the two organizations to deceive the recipient into executing the attached VBA script. Upon access to the victim’s Skype account, the attackers hijack an existing messaging thread and craft the naming convention of the files to relate to the context of the chat history.

The message sent to the victims from a compromised Skype account contains a VBS script with a filename following the following format: <filename.pdf> www.skype[.]vbs. The format is used to to trick the user into believing the file is a .PDF document instead of a VBA script (www.skype[.]vbs).

“Researchers from Truesec documented a similar DarkGate technique in early September. While the Skype routine masqueraded the VBS file as a PDF document, in the Teams version of compromise, the attackers concealed a .LNK file instead. Moreover, the sample that abused Teams came from an unknown, external sender.” continues Trend Micro.

Most of DarkGate attacks were observed in the Americas region, followed closely by those in Asia, the Middle East, and Africa. 

Trend Micro warns that the introduction of any new application to an organization must be carefully scrutinized because it can potentially enlarge the attack surface. 

“Cybercriminals can use these payloads to infect systems with various types of malware, including info stealers, ransomware, malicious and/or abused remote management tools, and cryptocurrency miners.” concludes the report.

“As long as external messaging is allowed, or abuse of trusted relationships via compromised accounts is unchecked, then this technique for initial entry can be done to and with any instant messaging (IM) apps.”

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Pierluigi Paganini

(SecurityAffairs – hacking, DarkGate)