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Persistence via Shell Extensions

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Test004

Persistence via Shell Extensions

Into to Windows Shell

The windows shell is the Graphical User Interface for the Windows Operating System, which includes the following:

  • Desktop
  • Start Menu
  • Taskbar
  • Etc.

Shell Development

"The Windows UI provides users with access to a wide variety of objects necessary to run applications and manage the operating system." 

- Some guy at microsoft

Includes but not limited to:

  • implementing custom file formats
  • implementing control panel items
  • implementing in-process extensions
  • Shell Extensibility (creating a data source)

We will be focusing on shell extensibility ... (Shell Extensions)

Shell Extensibility

Shell Extension Handlers

  • Shell capabilities can be extended with registry entries and .ini files

  • Shell Extension handlers impliment actions a shell can perform

    • example: Drop Handler - Called when an object is dragged over or dropped on a file

Shell Extension Handler Examples (file type association)

  • Shortcut Menu Handler
  • Data Handler
  • Drop Handler
  • Icon Handler
  • Property Sheet Hndler
  • Thumbnail Image Handler
  • Infotip Handler
  • Metadata Handler

Shell Extension Handler Examples (non file type association)

  • Column Handler (XP and earlier)
  • Copy hook handler
  • Drag and Drop handler
  • Icon Overlay Handler
  • Search Handler (XP and earlier)

More on Handlers (Handlers++)

"Many Shell extension handlers are in-process Component Object Model (COM) objects. They must be assigned a GUID and registered as described in Registering Shell Extension Handlers."

- Probably the same dude from microsoft
  • SO... all extensions must implement IUknown interface

Basic COM Primer 1

  • What is COM (Component Object Model)?

    • method for sharing binary code across applications

  • COM creates a binary standard (modules compiled in a specific structure) so that modules can be accessed from any programming language

Basic COM Primer 2

  • Interface?

    • Group of functions called methods
    • Interface names start with I as in IUnknown

  • COClass?

    • Component Object Class: contained in DLL / EXE
    • COClass impliments interfaces
    • COM object is na instance of COClass in memory

  • COM Server?

    • Binary containing one or more coclasses.

  • GUID?

    • Globally Unique Identifier: Unique 128 bit number
    • each interface and coclass has a GUID

Basic COM Primer 3

  • Instances created using CoCreateInstance method
  • Instances released using Release method defined in IUnknown

IUnknown:

  • AddRef() : increment reference count
  • Release() : decrement reference count
  • QueryInterface() : requests interface pointer from COM Object (used when coclass implements more than one interface)

Back to Shell Extensions

  • When X action happens our Y dll gets loaded

  • Handlers included in this project:

    • IconOverlay Handler
    • IconHandler (file specific)
    • Drop Handler
    • Property Sheet Handler (file specific)
    • Thumbnail Image Handler (file specific)
    • Infotip Handler (file specific)
    • Copy Hook Handler
    • Data Handler (file specific)

IconOverlay Handler

  • Interfaces:
    • IUnknown
    • IShellIconOverlayIdentifier
      • GetOverlayInfo: Provides the location of the icon overlay's bitmap.
      • GetPriority: Specifies the priority of an icon overlay.
      • IsMemberOf: Specifies whether an icon overlay should be added to a Shell object's icon.

IconHandler

  • Interfaces:

    • IUnknown
    • IPersistFile
      • GetCurFile: Retrieves the current name of the file associated with the object. If there is no current working file, this method retrieves the default save prompt for the object.
      • IsDirty: Determines whether an object has changed since it was last saved to its current file.
      • Load: Opens the specified file and initializes an object from the file contents.
      • Save: Saves a copy of the object to the specified file.
      • SaveCompleted: Notifies the object that it can write to its file.
    • IExtractIcon
      • Extract: Extracts an icon image from the specified location
      • GetIconLocation: Gets the location and index of an icon.

  • Very thorough tutorial on writing Icon Handlers. Shoutout to Pavel!

Drop Handler

  • Interfaces:
    • IUnknown
    • IPersistFile
      • GetCurFile: Retrieves the current name of the file associated with the object. If there is no current working file, this method retrieves the default save prompt for the object.
      • IsDirty: Determines whether an object has changed since it was last saved to its current file.
      • Load: Opens the specified file and initializes an object from the file contents.
      • Save: Saves a copy of the object to the specified file.
      • SaveCompleted: Notifies the object that it can write to its file.
    • IDropTarget
      • DragEnter: Indicates whether a drop can be accepted, and, if so, the effect of the drop.
      • DragLeave: Removes target feedback and releases the data object.
      • DragOver: Provides target feedback to the user and communicates the drop's effect to the DoDragDrop function so it can communicate the effect of the drop back to the source.
      • Drop: Incorporates the source data into the target window, removes target feedback, and releases the data object.

Property Sheet Handler (file specific)

  • Interfaces:
    • IUnknown
    • IShellExtInit
      • Initialize: Initializes a property sheet extension, shortcut menu extension, or drag-and-drop handler.
    • IShellPropSheetExt
      • AddPages: Adds one or more pages to a property sheet that the Shell displays for a file object. The Shell calls this method for each property sheet handler registered to the file type.
      • ReplacePage: Replaces a page in a property sheet for a Control Panel object.

Thumbnail Image Handler (file specific)

  • Interfaces

Infotip Handler (file specific)

  • Interfaces:
    • IUnknown
    • IQueryInfo:
      • GetInfoFlags: Gets the information flags for an item. This method is not currently used.
      • GetInfoTip: Gets the info tip text for an item.

Copy Hook Handler

  • Interfaces:
    • IUnknown
    • ICopyHook:
      • CopyCallback: Called to approve or deny copy operation

Data Handler (file specific)

  • Interfaces:
    • IUnknown
    • IPersistFile
      • GetCurFile: Retrieves the current name of the file associated with the object. If there is no current working file, this method retrieves the default save prompt for the object.
      • IsDirty: Determines whether an object has changed since it was last saved to its current file.
      • Load: Opens the specified file and initializes an object from the file contents.
      • Save: Saves a copy of the object to the specified file.
      • SaveCompleted: Notifies the object that it can write to its file.
    • IDataObject:
      • 9 methods which I will not include here... click interface link for more details

All About Hijacking

  • Installing all these handlers requires Admin privilges

    • Requires writes to:
      • HKEY_LOCAL_MACHINE (IconOverlay)
      • HKEY_CLASSES_ROOT (Other Handlers such as file type specific)
    • Privileged can be noisy

  • COM Objects vulnerable to COM Hijacking!

    • Since all these extensions require COM, they are vulnerable to COM Hijacking
    • COM hijacking doesn't require admin privs
      • Regestry writes needed for HKEY_CURRENT_USER\Software\Classes\CLSID\
        • add key
        • set dll path
        • set ThreadingModel (apartment)

  • More on COM Hijacking

More References

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Persistence via Shell Extensions

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