Beware of Weaponized TeamViewer Installer that Delivers njRAT

Threat actors relying on legitimate, well-known software TeamViewer for exploitation has been a very common scenario.

There have been several cases where threat actors used well-known software to deliver malware to the victims.

Similarly, a recent report from Cyble Research & Intelligence Labs stated that the most popularly used remote desktop support software, “TeamViewer” has been exploited by threat actors to deliver njRAT malware.

Other software that was delivering njRAT malware include Wireshark, Process Hacker, etc.,

njRAT is a remote access trojan that can perform keylogging, password stealing, data exfiltration, accessing webcams, and microphones, downloading additional files, and many others.

It was first discovered in 2012 and was attacking organizations in Middle Eastern nations. 

Weaponized TeamViewer Installer

The Initial level of compromise for njRAT involves traditional methods like phishing campaigns, cracked software on file-sharing websites, and drive-by downloads. In addition to this, the malware is now being distributed via trojanized applications.

Once the malware is executed, it drops two files on the C:\Windows folder in which, one of them is the njRAT malware.

The Installer then triggers the malware “TeamViewer Starting.exe” and eventually launches the legitimate “teamviewer.exe” application.

During the installation of TeamViewer, njRAT simultaneously starts the installation by copying itself to the \AppData\Local\Temp folder with the name “system.exe.”

It then executes the newly dropped file, and njRAT creates a mutex.

Post Exploitation and Persistence

njRAT modifies the “SEE_MASK_NOZONECHECKS” environment variable in Windows, which prevents security warning prompts or dialog boxes from being presented to the user, thereby operating without any hindrance.  

Furthermore, the malware also changes the Firewall regulation to allow communications with the C2 (Command and Control) server. 

The malware creates two autorun entries in the system registry to maintain persistence in the system. 

The malware then collects information about Keystrokes, Windows OS version, service pack, webcam information, the current date, username, system architecture, and specific registry keys.

It stores all of this information in the “%appdata%/temp” folder under the filename “System.exe.tmp”.

Indicators of Compromise

Indicators	Description
224ae485b6e4c1f925fff5d9de1684415670f133f3f8faa5f23914c78148fc31	Trojanized Teamviewer
9b9539fec7d0227672717e126a9b46cda3315895
11aacb03c7e370d2b78b99efe9a131eb
9bcb093f911234d702a80a238cea14121c17f0b27d51bb023768e84c27f1262a	system.exe/ TeamViewer Starting.exe
b2f847dce91be5f5ea884d068f5d5a6d9140665c
8ccbb51dbee1d8866924610adb262990
hxxp://kkk[.]no-ip[.]biz	C&C