Adversaries may execute their own malicious payloads by hijacking how the .NET AppDomainManager loads assemblies. The .NET framework uses the AppDomainManager class to create and manage one or more isolated runtime environments (called application domains) inside a process to host the execution of .NET applications. Assemblies (.exe or .dll binaries compiled to run as .NET code) may be loaded into an application domain as executable code.[1]
Known as "AppDomainManager injection," adversaries may execute arbitrary code by hijacking how .NET applications load assemblies. For example, malware may create a custom application domain inside a target process to load and execute an arbitrary assembly. Alternatively, configuration files (.config) or process environment variables that define .NET runtime settings may be tampered with to instruct otherwise benign .NET applications to load a malicious assembly (identified by name) into the target process.[2][3][4]
| ID | Mitigation | Description |
|---|---|---|
| M1022 | Restrict File and Directory Permissions |
Install .NET applications and related software in write-protected locations. Set directory access controls to prevent file writes to the search paths for .NET applications, both in the folders where applications are run from and the standard resources folders. |
| ID | Data Source | Data Component | Detects |
|---|---|---|---|
| DS0022 | File | File Creation |
Monitor for newly constructed files, especially unknown .NET assemblies and configuration files in user writable folder paths. |
| DS0011 | Module | Module Load |
Monitor DLL/PE file events, specifically creation of these binary files as well as the loading of .NET assemblies into processes (which may not always create standard image load events). Look for image loads that are not recognized or not normally loaded into a process.[2][4] |
| DS0009 | Process | Process Creation |
Monitor newly constructed processes for unusual activity (e.g., a process that does not use the network begins to do so) as well as the loading of unexpected .NET resources. |