Behavior:Win32/SuspFileWrite.V

The core of Behavior:Win32/SuspFileWrite revolves around a specific and suspicious file-writing sequence. Analysis of associated samples reveals a common technical pattern. The process, which is often a downloaded binary file from the internet, will create a new folder within a temporary directory, such as %Temp%\ or %AppData%, with a randomly generated name. Subsequently, it writes one or more binary (.exe) and dynamic link library (.dll) files into this newly created directory. For instance, a typical infection chain involves the creation of a file like %Temp%\crs\<random_folder>\setup.exe. 

These dropped files are frequently the actual PUPs or malware payloads. To establish persistence and ensure launching upon system startup, the Behavior:Win32/SuspFileWrite creates or modifies Windows Registry entries. A prevalent method observed is the creation of a Run key, such as HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run, with a value pointing to the path of the dropped malicious binary. The initial dropper process may also make outbound network connections to download these additional payloads.  

Specific IP addresses and URLs associated with these activities are dynamic, but historical campaigns have involved connections to domains like cdn-[random-string][.]org and IPs such as 185[.]189.116[.]101 to retrieve the secondary payloads. The downloaded files often have innocuous-sounding names like mediaplayer.exe or update.exe to evade user suspicion.