caseysmithrc
50 lines
2.8 KiB
Markdown
50 lines
2.8 KiB
Markdown
# T1042 - Change Default File Association
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## [Description from ATT&CK](https://attack.mitre.org/wiki/Technique/T1042)
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<blockquote>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. (Citation: Microsoft Change Default Programs) (Citation: Microsoft File Handlers) 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.
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System file associations are listed under <code>HKEY_CLASSES_ROOT\.[extension]</code>, for example <code>HKEY_CLASSES_ROOT\.txt</code>. The entries point to a handler for that extension located at <code>HKEY_CLASSES_ROOT\[handler]</code>. The various commands are then listed as subkeys underneath the shell key at <code>HKEY_CLASSES_ROOT\[handler]\shell\[action]\command</code>. For example:
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*<code>HKEY_CLASSES_ROOT\txtfile\shell\open\command</code>
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*<code>HKEY_CLASSES_ROOT\txtfile\shell\print\command</code>
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*<code>HKEY_CLASSES_ROOT\txtfile\shell\printto\command</code>
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The values of the keys listed are commands that are executed when the handler opens the file extension. Adversaries can modify these values to execute arbitrary commands.
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Detection: 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.
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User file association preferences are stored under <code> [HKEY_CURRENT_USER]\Software\Microsoft\Windows\CurrentVersion\Explorer\FileExts</code> and override associations configured under <code>[HKEY_CLASSES_ROOT]</code>. Changes to a user's preference will occur under this entry's subkeys.
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Also look for abnormal process call trees for execution of other commands that could relate to Discovery actions or other techniques.
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Platforms: Windows
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Data Sources: Windows Registry, Process command-line parameters, Process monitoring
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Permissions Required: User, Administrator, SYSTEM
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Contributors: Stefan Kanthak, Travis Smith, Tripwire</blockquote>
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## Atomic Tests
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- [Atomic Test #1 - Change Default File Association](#atomic-test-1---change-default-file-association)
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<br/>
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## Atomic Test #1 - Change Default File Association
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Change Default File Association From cmd.exe
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**Supported Platforms:** Windows
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#### Inputs
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| Name | Description | Type | Default Value |
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|------|-------------|------|---------------|
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| extension_to_change | File Extension To Hijack | String | .wav|
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| target_exenstion_handler | Thing To Open | Path | C:\Program Files\Windows Media Player\wmplayer.exe|
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#### Run it with `command_prompt`!
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```
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cmd.exe assoc #{extension_to_change}="#{thing_to_execute}"
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```
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<br/>
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