Microsoft Visual Studio add-ins could be used to deliver malware

Following the demise of macros in Microsoft Office files, it seems that another alternative method is gaining popularity, new reports have claimed.

Cybersecurity researchers from Deep Instinct have discovered an uptick in the use of Microsoft Visual Studio Tools for Office (VSTO) among cybercriminals, as they build malicious Office add-ins which help them achieve persistence and run malicious code on target endpoints.

What hackers are doing here is building .NET-based malware, and then embedding it into an Office add-in, a practice that requires the threat actor to be somewhat more skilled. 

Bypassing antivirus

The method is hardly new but wasn’t as popular while Office macros were dominating. Now that Microsoft effectively eliminated that threat, VSTO-built threats are emerging in greater numbers. These add-ins can be sent together with Office documents, or hosted elsewhere and triggered by an Office document sent by the attackers. 

In other words, the victim still needs to download and run an Office file and the add-in in order to get infected, so phishing will still play a major role. That being said, the attack vector is still quite dangerous as it is capable of successfully working around antivirus programs and other malware protection services. In fact, Deep Instinct was able to create a working Proof-of-Concept (PoC) that delivered the Meterpreter payload to the endpoint. The video demonstration of the PoC can be found on this link. The researchers said they were forced to disable Microsoft Windows Defender just to record the process. 

Meterpreter, a security product used for penetration testing, was easy for antivirus products to detect, however, all the elements of the PoC were not detected, they said.

In conclusion, the researchers expect the number of VSTO-built attacks to continue rising. They also expect nation-states and other “high caliber” actors to adopt the practice as well.

Via: BleepingComputer

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