What is AlwaysInstallElevated and how does it enable privilege escalation?

AlwaysInstallElevated is a Group Policy configuration that, when enabled, allows standard users to execute MSI installation files with SYSTEM privileges. To enable it, you must set both `Computer Configuration\Administrative Templates\Windows Components\Windows Installer` and `User Configuration\Administrative Templates\Windows Components\Windows Installer` to "Enabled", or create corresponding registry keys under `HKLM` and `HKCU`. Once enabled, a standard user can run `msiexec /q /i malicious.msi` to execute arbitrary code as SYSTEM, as detailed in the article Test Analysis of Privilege Escalation Using AlwaysInstallElevated.