The .NET runtime is the execution environment that runs managed Windows applications. It provides services such as memory management, type safety, assembly loading, JIT compilation, and startup configuration through files, environment variables, and runtime settings. In practice, it decides how a .NET program begins execution and which code it loads first.
That makes the runtime an attractive target for attackers. If they can alter startup settings, redirect assembly resolution, or abuse configuration features such as AppDomain behavior, they may cause a trusted application to load malicious code while still appearing legitimate. Defenders watch for unusual runtime files, unexpected DLL or assembly loads, writable application directories, and suspicious changes to process startup behavior. Hardening the runtime path helps stop sideloading, configuration tampering, and other attacks that hide inside normal software execution.