The Meterpreter Payload is a specific type of multi-faceted, extensible Payload that uses DLL injection to ensure the connection to the victim host is stable and difficult to detect using simple checks and can be configured to be persistent across reboots or system changes. Furthermore, Meterpreter resides entirely in the memory of the remote host and leaves no traces on the hard drive, making it difficult to detect with conventional forensic techniques.

It is dubbed the swiss army knife of pentesting, and for a good reason. The purpose of Meterpreter is to specifically improve our post-exploitation procedures, offering us a hand-picked set of relevant tools for more straightforward enumeration of the target host from the inside. It can help us find various privilege escalation techniques, AV evasion techniques, further vulnerability research, provide persistent access, pivot, etc.

For some interesting reading, check out this post on Meterpreter stageless payloads and this post on modifying Metasploit templates for evasion. These topics are outside the scope of this module, but we should be aware of these possibilities.

Running Meterpreter

To run Meterpreter, we only need to select any version of it from the show payloads output, taking into consideration the type of connection and OS we are attacking.

When the exploit is completed, the following events occur:

• The target executes the initial stager. This is usually a bind, reverse, findtag, passivex, etc.
• The stager loads the DLL prefixed with Reflective. The Reflective stub handles the loading/injection of the DLL.
• The Meterpreter core initializes, establishes an AES-encrypted link over the socket, and sends a GET. Metasploit receives this GET and configures the client.
• Lastly, Meterpreter loads extensions. It will always load stdapi and load priv if the module gives administrative rights. All of these extensions are loaded over AES encryption.

Whenever the Meterpreter Payload is sent and run on the target system, we receive a Meterpreter shell. We can then immediately issue the help command to see what the Meterpreter shell is capable of.

MSF - Meterpreter Commands

Meterpreter

meterpreter > help

Core Commands
=============

    Command                   Description
    -------                   -----------
    ?                         Help menu
    background                Backgrounds the current session
    bg                        Alias for background
    bgkill                    Kills a background meterpreter script
    bglist                    Lists running background scripts
    bgrun                     Executes a meterpreter script as a background thread
    channel                   Displays information or control active channels
    close                     Closes a channel
    disable_unicode_encoding  Disables encoding of unicode strings
    enable_unicode_encoding   Enables encoding of unicode strings
    exit                      Terminate the meterpreter session
    get_timeouts              Get the current session timeout values
    guid                      Get the session GUID
    help                      Help menu
    info                      Displays information about a Post module
    irb                       Open an interactive Ruby shell on the current session
    load                      Load one or more meterpreter extensions
    machine_id                Get the MSF ID of the machine attached to the session
    migrate                   Migrate the server to another process
    pivot                     Manage pivot listeners
    pry                       Open the Pry debugger on the current session
    quit                      Terminate the meterpreter session
    read                      Reads data from a channel
    resource                  Run the commands stored in a file
    run                       Executes a meterpreter script or Post module
    secure                    (Re)Negotiate TLV packet encryption on the session
    sessions                  Quickly switch to another session
    set_timeouts              Set the current session timeout values
    sleep                     Force Meterpreter to go quiet, then re-establish session.
    transport                 Change the current transport mechanism
    use                       Deprecated alias for "load"
    uuid                      Get the UUID for the current session
    write                     Writes data to a channel

Some of these commands are also available in the module cheat sheet for reference.

The main idea we need to get about Meterpreter is that it is just as good as getting a direct shell on the target OS but with more functionality. The developers of Meterpreter set clear design goals for the project to skyrocket in usability in the future. Meterpreter needs to be:

• Stealthy
• Powerful
• Extensible