This module exploits an authentication bypass in Veeam.Backup.ServiceLib.CForeignInvokerNegotiateAuthenticator.Authenticate. Then a file upload present in ExecuteUploadManagerPerformUpload is used to copy the Web.config file to the Webapp root foler in order to extract the machineKey values to create a ysoserial.NET payload to execute commands. The deployed agent will run with the privileges of the "IIS Worker Process" process (NT AUTHORITY\\NETWORK SERVICE).
This module uses a path confusion that leads to an authentication bypass (ACL) which allows unauthenticated access to an arbitrary backend URL. Then an elevation of privilege present in CommonAccessTokenFromUrl of RemotePowershellBackendCmdletProxyModule.cs is used to execute Exchange powershell commands as Exchange Administrator. Finally, an arbitrary file write present in the New-MailboxExportRequest Exchange powershell command is used to write a webshell in the system file. The deployed agent will run with the SYSTEM privileges.