A newly discovered phishing campaign is exploiting the Follina security vulnerability to deploy a private backdoor, named Rozena on the Windows systems.
"Rozena is a backdoor malware that is capable of injecting a remote shell connection back to the attacker's machine," Cara Lin, a researcher at Fortinet FortiGuard Labs stated in a report published this week.
Tracked as CVE-2022-30190, the security bug is related to the Microsoft Support Diagnostic Tool (MSDT) that impacts Windows 7, Windows 8.1, Windows 10, Windows 11, Windows Server 2008, Windows Server 2012, Windows Server 2016, Windows Server 2019, and Windows Server 2022. The vulnerability came to light in late May 2022 but the root cause of the flaw has been known for at least a couple of years.
The latest attack chain is a weaponized Office document that, when opened, links to a Discord CDN URL to retrieve an HTML file ("index.htm") that, in turn, triggers the diagnostic utility employing a PowerShell command to download next-stage payloads from the same CDN attachment space.
This includes the Rozena implant ("Word.exe") and a batch file ("cd.bat") that's designed to terminate MSDT processes, establish the backdoor's persistence by means of Windows Registry modification, and download a harmless Word document as a decoy.
The primary function of the Rozena backdoor is to inject a shellcode that launches a reverse shell to the hacker’s device (“microsofto.duckdns[.]org”), in this way the malicious actor can secure full control of the system.
The exploitation of the Follina security bug is done by distributing the malware via malicious word documents. The word documents act as a dropper and are distributed through emails that contains a password-encrypted ZIP as an attachment, an HTML file, and a link to download, in the body of the email. Multiple malware such as Emotet, QBot, IcedID, and Bumblebee are then injected into the victim’s device.
According to researchers, the assaults discovered in early April primarily featured Excel files with XLM macros. Microsoft's decision to block macros by default around the same time is said to have forced the hackers to shift to alternative techniques like HTML smuggling as well as .LNK and .ISO files.
“CVE-2022-30190 is a high-severity vulnerability that lets a malicious actor deliver malware through an MS Word document. Microsoft already released a patch for it on June 14, 2022. In this blog, we showed how an attacker exploits Follina and included details of Rozena and the SGN ShellCode. Users should apply the patch immediately and also apply FortiGuard protection to avoid the threat,” the researcher concluded.
