T1546.001: Change Default File Association
Adversaries may establish persistence by executing malicious content triggered by a file type association. When a file is opened, the default program used to open the file (also called the file association or handler) is checked. File association selections are stored in the Windows Registry and can be edited by users, administrators, or programs that have Registry access or by administrators using the built-in assoc utility. Applications can modify the file association for a given file extension to call an arbitrary program when a file with the given extension is opened.
System file associations are listed under HKEY_CLASSES_ROOT.[extension]
, for example HKEY_CLASSES_ROOT.txt
. The entries point to a handler for that extension located at HKEY_CLASSES_ROOT\[handler]
. The various commands are then listed as subkeys underneath the shell key at HKEY_CLASSES_ROOT\[handler]\shell\[action]\command
. For example:
HKEY_CLASSES_ROOT\txtfile\shell\open\command
HKEY_CLASSES_ROOT\txtfile\shell\print\command
HKEY_CLASSES_ROOT\txtfile\shell\printto\command
The values of the keys listed are commands that are executed when the handler opens the file extension. Adversaries can modify these values to continually execute arbitrary commands.
Positive Technologies products that cover the technique
MaxPatrol SIEM knowledge base
mitre_attck_persistence: PT-CR-664: Default_File_Association_Modify: The process changed one of the registry branches responsible for determining the default application used to open files with a specific extension in the system
Detection
ID | DS0009 | Data source and component | Process: Process Creation | Description | Monitor for newly executed processes that may establish persistence by executing malicious content triggered by a file type association. |
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ID | DS0024 | Data source and component | Windows Registry: Windows Registry Key Modification | Description | Collect and analyze changes to Registry keys that associate file extensions to default applications for execution and correlate with unknown process launch activity or unusual file types for that process. User file association preferences are stored under |
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ID | DS0017 | Data source and component | Command: Command Execution | Description | Monitor executed commands and arguments that may establish persistence by executing malicious content triggered by a file type association. |
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