The MSI installer for Splashtop Streamer for Windows before 3.5.8.0 uses a temporary folder with weak permissions during installation. A local user can exploit this to escalate privileges to SYSTEM by placing a wevtutil.exe file in the folder.
The C:\Program Files (x86)\Splashtop\Splashtop Software Updater\uninst.exe process creates a folder at C:\Windows\Temp~nsu.tmp and copies itself to it as Au_.exe. The C:\Windows\Temp~nsu.tmp\Au_.exe file is automatically launched as SYSTEM when the system reboots or when a standard user runs an MSI repair using Splashtop Streamer’s Windows Installer. Since the C:\Windows\Temp~nsu.tmp folder inherits permissions from C:\Windows\Temp and Au_.exe is susceptible to DLL hijacking, standard users can write a malicious DLL to it and elevate their privileges.