curlbomb 1.4.1
A personal HTTP server for serving one-time-use shell scripts
License: MIT

curlbomb
========

curlbomb is a personal HTTP(s) server for serving one-time-use shell
scripts.

You know all those docs for the cool and hip software projects that
start out by telling you to install their software in one line, like
this?

::

    curl http://example.com/install.sh | bash

I call that a curl bomb... I don't know if anyone else does.

*convenient* as hell, but a security and trustability *nightmare*.
Especially since installers usually require root access, do you trust a
random file on the internet with direct access to your machine?

But I usually try to ask myself this question: is it possible to turn a
*bad* idea into a *good* one, or at the very least a less-bad idea?
Let's take a look..

curlbomb serves a single file (read from disk or stdin) via HTTP to the
first client to request it, then it shuts down. A command is printed out
that will construct the curl bomb the client needs to run, which
includes a one-time-use passphrase (called a knock) that is required to
download the resource. This command is copy/pasted (or typed) into
another shell, on some other computer, which will download and run the
script in one line.

curlbomb has optional (but recommended) integration with OpenSSL to
secure communications. OpenSSH is supported as well, to make it easy to
curlbomb from anywhere on the internet, to anywhere else, through a
proxy server that you can forward the port through.

So does curlbomb measure up to making this a good idea? Decide for
yourself:

+----------+------------------------+----------+
| Feature/ | Traditional curl bomb  | Using    |
| Problem  |                        | curlbomb |
+==========+========================+==========+
| Convenie | Yup, sure is.          | I think  |
| ce       |                        | so.      |
+----------+------------------------+----------+
| Trust    | Is it even SSL? Do you | Self     |
|          | know/trust the URL and | hosted   |
|          | it's author?           | server   |
|          |                        | and SSL  |
|          |                        | verifies |
|          |                        | connecti |
|          |                        | on       |
+----------+------------------------+----------+
| Security | Even if you verify the | Self     |
|          | script beforehand,     | hosted   |
|          | `are you sure it       | script,  |
|          | hasn't                 | you're   |
|          | changed? <https://www. | in       |
|          | idontplaydarts.com/201 | control  |
|          | 6/04/detecting-curl-pi | of the   |
|          | pe-bash-server-side/>` | contents |
|          | __                     | .        |
+----------+------------------------+----------+
| Privacy  | Anyone who knows the   | curlbomb |
|          | URL can download/run.  | requires |
|          | Cannot contain private | a        |
|          | information like       | passphra |
|          | passwords.             | se       |
|          |                        | (knock)  |
|          |                        | and only |
|          |                        | serves a |
|          |                        | file one |
|          |                        | time (by |
|          |                        | default. |
|          |                        | )        |
|          |                        | Optional |
|          |                        | ly       |
|          |                        | gpg      |
|          |                        | encrypt  |
|          |                        | the      |
|          |                        | contents |
|          |                        | of the   |
|          |                        | script.  |
|          |                        | Put      |
|          |                        | sensitiv |
|          |                        | e        |
|          |                        | data     |
|          |                        | like SSH |
|          |                        | keys and |
|          |                        | passphra |
|          |                        | ses      |
|          |                        | into     |
|          |                        | your     |
|          |                        | script   |
|          |                        | as       |
|          |                        | necessar |
|          |                        | y.       |
+----------+------------------------+----------+
| Repeatab | Is the script going to | It's     |
| ility    | stay at the same URL   | your     |
|          | forever? Can you       | script,  |
|          | specify any parameters | read     |
|          | or at least a version  | whatever |
|          | number?                | env vars |
|          |                        | you      |
|          |                        | want.    |
|          |                        | You can  |
|          |                        | keep it  |
|          |                        | checked  |
|          |                        | into     |
|          |                        | your own |
|          |                        | git      |
|          |                        | reposito |
|          |                        | ry       |
|          |                        | and      |
|          |                        | serve it |
|          |                        | from     |
|          |                        | anywhere |
|          |                        | anytime. |
+----------+------------------------+----------+

curlbomb is well tested, but not intended for heavy automation work.
There are better alternatives to choose from (saltstack, ansible,
puppet, etc.) curlbomb can be used effectively in doing the front work
for setting up these other tools, like copying SSH keys and installing
packages.

Install
-------

curlbomb can be installed from the `Arch User
Repository <https://aur.archlinux.org/packages/curlbomb/>`__ (AUR):

::

    pacaur -S curlbomb

Or from the `Python Package
Index <https://pypi.python.org/pypi/curlbomb>`__ (PyPI):

::

    pip install curlbomb

Dependencies
~~~~~~~~~~~~

-  Python 3.5 (I haven't tested anything lower)
-  `Tornado <http://www.tornadoweb.org/>`__
-  `Requests <https://pypi.python.org/pypi/requests>`__
-  `psutil <https://pypi.python.org/pypi/psutil/>`__
-  OpenSSL (optional, if using --ssl)
-  OpenSSH (optional, if using --ssh)
-  GnuPG (optional, if using encrypted SSL cert or resources)
-  `python-notify2 <https://pypi.python.org/pypi/notify2>`__ (optional,
   for desktop notifications when using ping subcommand)
-  curl (on the client machine, preferably version >= 7.39.0, for
   --pinnedpubkey support)

Example Use
-----------

Serve a script stored in a file:

::

    curlbomb run /path/to/script

This outputs a curl command that you copy and paste into a shell on
another computer:

::

    KNOCK=nDnXXp8jkZKtbush bash <(curl -LSs http://192.0.2.100:48690)

Once pasted, the script is automatically downloaded and executed.

By default, the client must pass a KNOCK variable that is passed in the
HTTP headers. This is for two reasons:

-  It adds a factor of authentication. Requests without the knock are
   denied.
-  It helps to prevent mistakes, as the knock parameter is randomly
   generated each time curlbomb is run and can only be used once. (See
   ``-n 1``)

(Astute readers will notice that the KNOCK variable is being fed to the
script that is being downloaded, not into the curl command. That's
because it's really a curlbomb within a curlbomb. The first curl command
downloads a script that includes a second curl command that *does*
require the KNOCK parameter. This nesting allows us to keep the client
command as short as possible and hide some extra boilerplate. See
``--unwrapped``.)

If you want just the curl, without the bomb, ie. you just want to grab
the script without redirecting it to bash, use ``--survey``. This is
useful for testing the retrieval of scripts without running them.

You can pipe scripts directly into curlbomb:

::

    echo "pacman --noconfirm -S openssh && systemctl start sshd" | curlbomb

Whenever you pipe data to curlbomb you can omit the ``run`` subcommand,
it's assumed that you want to run a script from stdin.

This works in shell scripts too:

::

    cat <<EOF | curlbomb
    #!/bin/bash
    echo "I'm a script output from another script on another computer"
    EOF

Or type it interactively:

::

    $ curlbomb run -
    pkg instll sqlite3
    echo "bad idea, I don't have spollcheck when I typ in the terminal"

(The single dash says to read from stdin, even when nothing is being
piped. Ctrl-D ends the interactive input.)

The shebang line (#!) is interpreted and automatically changes the
interpreter the client runs, the following example runs the script with
python instead of the default bash:

::

    cat <<EOF | curlbomb
    #!/usr/bin/env python3
    import this
    print("Hello, from Python!")
    EOF

curlbomb can also transfer files and directories with ``put`` and
``get`` subcommands:

::

    # Recursively copy a directory 
    # (to whatever directory the client is run from):
    curlbomb put ~/.ssh

    # Recursively copy a remote directory to the server
    # (to whatever directory the server is run from)
    curlbomb get /var/log 

    # Recursively copy a directory
    #  - Specifies the explicit remote destination directory.
    #  - Environment vars in single quotes are evaluated on the remote end.
    #  - Excludes some files you may want to keep private.
    curlbomb put ~/.ssh '$HOME' --exclude='*rsa'

The ``put`` and ``get`` subcommands are just convenience wrappers for
running tar on both ends of the curlbomb pipe. You *could* achieve the
same thing more generically:

::

    # Copy a local directory to a client, the hard way:
    tar cjh -C $HOME .ssh | curlbomb run -c "tar xjv -f"

    # Copy a remote directory to the server, the hard way:
    echo "tar cjh -C /var log" | curlbomb -l --client-quiet | tar xjv

The first example has a ``run -c`` parameter that tells the client that
we want to interpret the data as being a tar archive rather than a
script. The second example has a ``-l`` parameter that will output the
data received to stdout, in this case piped directly into tar.

SSH tunnel
~~~~~~~~~~

By default, curlbomb constructs URLs with the IP address of the local
machine. This usually means that clients on another network will be
unable to retrieve anything from curlbomb, unless you have a port opened
up through your firewall (and appropriate use of the ``--domain`` and
``--port`` arguments.) As an alternative, curlbomb can be tunneled
through SSH to another host that has the proper port open. For instance:

::

    echo "apt-get install salt-minion" | curlbomb --ssh user@example.com:8080

The above command connects to example.com over SSH (port 22 by default)
and forwards the curlbomb server port to example.com:8080. The URL that
curlbomb prints out will now use the domain name of the ssh server,
instead of the local IP address. The SSH tunnel is left open for as long
as the curlbomb server remains running. Any user directly on the
example.com host will be able to fetch the resource from localhost:8080.
However, by default, SSH does not open this up to the rest of the world.
If you want any client to be able to connect to example.com:8080 you
will need to modify the sshd\_config of the server to allow
GatewayPorts:

::

    # Put this in your /etc/ssh/sshd_config and restart your ssh service:
    GatewayPorts clientspecified

TLS / SSL security
~~~~~~~~~~~~~~~~~~

For extra security, you can enable TLS with ``--ssl``:

::

    echo "PASSWORD=hunter2 run_my_server" | curlbomb --ssl /path/to/cert.pem

The example above is passing a bit of secure information; a password.
Even without TLS, curlbomb secures access with a knock parameter. For
many use-cases, this is sufficient to secure it, as curlbombs are short
lived and can only be retrieved one time (``-n 1``). However, the
connection itself might be spied on (or even modified!) through traffic
analysis at your ISP or any other router your connection flows through.
Using TLS makes sure this doesn't happen.

Note that when the ``--ssl`` parameter is combined with the ``--ssh``
parameter, the SSL certificate should be generated for the host running
the SSH server rather than the one running curlbomb. To prevent having
to store the SSL certificate in plain text on your local machine, the
file may be optionally PGP encrypted and curlbomb will decrypt it only
when necessary.

You can also specify the SSL certificate path as a single ``-``. In this
case, a new self-signed certificate will be generated and used for this
session only.

``--pin`` can be used to extract the SSL certificate fingerprint and
directly provide it to the client curl command (requires curl >=7.39).
This avoids having to trust the client's CA root certificate store, and
trusts your certificate explicitly. When generating a self-signed
certificate with ``--ssl``, the ``--pin`` option is turned on
automatically. Pinning adds some extra security benefits, but makes the
client command you have to paste/type much longer than it usually is,
for example:

::

    $ echo "whoami" | curlbomb --ssl -
    WARNING:curlbomb.server:No SSL certificate provided, creating a new self-signed certificate for this session
    Paste this command on the client:

      KNOCK=bbxfOV1ToDVhJjAl bash <(curl -LSs -k --pinnedpubkey 'sha256//RSkhZc2Qw/j8AxHMLUzipRpegEK9I0BlX7J1I5bcg0Y=' https://192.0.2.100:39817)
      

``--pin`` is a different kind of trust model then using a certificate
signed by a CA. When you use ``--pin`` you are completely bypassing the
root CA certificate store of the client machine and instructing it to
trust your certificate explicitly. This mitigates many man-in-the-middle
type attacks that can happen with TLS, but you still need to take care
that the client command is not modified or eavesdropped before being
pasted into the client.

Aliases
~~~~~~~

By now the curlbomb command might be getting quite long. Once you've
encrypted and stored your SSL certificate, and setup your SSH server,
create an alias for ease of use, for example:

::

    alias cb=curlbomb --ssl ~/.curlbomb/curlbomb.pem.gpg --ssh user@example.com:22:8080

There's a few more examples in `EXAMPLES.md <EXAMPLES.md>`__

Command Line Args
-----------------

::

    curlbomb [-h] [-n N] [-p PORT] [-d host[:port]] [-w] [-l] [-q] [-v]
             [--ssh SSH_FORWARD] [--ssl CERTIFICATE] [--pin] [-e]
             [--encrypt-to GPG_ID] [--passphrase] [--survey] [--unwrapped]
             [--client-logging] [--client-quiet] [--mime-type MIME_TYPE]
             [--disable-knock] [--knock KNOCK] [--version]
             {run,put,get,ping,ssh-copy-id} ...
                   

curlbomb has a few subcommands:

-  ``run`` - run a shell script
-  ``put`` - copy local files/directories to remote system
-  ``get`` - copy remote files/directories to local system
-  ``ping`` - wait for a client to finish a task, with optional
   notification command
-  ``ssh-copy-id`` - copy SSH public keys to the remote authorized\_keys
   file

If no subcommand is specified, and there is data being piped to stdin,
then the ``run`` subcommand is used implicitly.

The following arguments apply to all subcommands:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

``-n N, --num-gets N`` The maximum number of times the script may be
fetched by clients, defaulting to 1. Increasing this may be useful in
certain circumstances, but please note that the same knock parameter is
used for all requests so this is inherently less secure than the
default. Setting this to 0 will allow the resource to be downloaded an
unlimited number of times.

``-p PORT`` The local TCP port number to use.

``-d host[:port], --domain host[:port]`` Specify the domain name and
port that is displayed in the URL of the client command. This does not
change where the resource is actually located, use --port or --ssh for
that. This is useful if you are setting up your own port forwards and
need to show an external URL.

``-w, --wget`` Print wget syntax rather than curl syntax. Useful in the
case where the client doesn't have curl installed. Not compatible with
``--log--posts`` or the ``put`` and ``get`` subcommands. :(

``-l, --log-posts`` Log the client stdout to the server stdout.

``-q, --quiet`` Be more quiet. Don't print the client curlbomb command.

``-v, --verbose`` Be more verbose. Turns off ``--quiet``, enables
``--log-posts``, and enables INFO level logging within curlbomb.

``--ssh SSH_FORWARD`` Forwards the curlbomb server to a remote port of
another computer through SSH. This is useful to serve curlbombs to
clients on another network without opening up any ports to the machine
running curlbomb. The syntax for SSH\_FORWARD is
[user@]host[:ssh\_port][:http\_port]. The SSH server must have the
GatewayPorts setting turned on to allow remote clients to connect to
this port. See sshd\_config(5).

``--ssl CERTIFICATE`` Run the HTTP server with TLS encryption. Provide
the full path to your SSL certificate, which may be PGP encrypted. The
file should contain the entire certificate chain, including the CA
certificate, if any. If the SSL certificate path is specified as ``-``,
a temporary self-signed certificate will be generated for the current
curlbomb session and ``--pin`` will be turned on implicitly.

``--pin`` (requires curl>=7.39.0) Pin the SSL certificate fingerprint
into the client curl command. This is used to bypass the root CA store
of the client machine, and to tell it exactly what the server's SSL
certificate looks like. This is useful for mitigating man-in-the-middle
attacks, as well as when using self-signed certificates. This makes the
client command quite a bit longer than usual.

``-e, --encrypt`` Encrypt the resource with gpg before serving it to the
client. A randomly generated symmetric passphrase will be printed below
the client command on the server. This passphrase must be input on the
client. You can specify the passphrase to use interactively with
``--passphrase``. You can use public key encryption if you use
``--encrypt-to``

``--passphrase`` Encrypt the resource with a passphrase interactively
asked on server start.

``--encrypt-to GPG_ID`` Encrypt the resource with the given gpg
identity. Can be specified multiple times to encrypt to multiple
recipients.

``--survey`` Only print the curl (or wget) command. Don't redirect to a
shell command. Useful for testing script retrieval without running them.

``--unwrapped`` output the full curlbomb command, including all the
boilerplate that curlbomb normally wraps inside of a nested curlbomb.

This parameter is useful when you want to source variables into your
current shell:

::

    echo "export PATH=/asdf/bin:$PATH" | curlbomb -c source --unwrapped

Without the --unwrapped option, the client command will not run the
source command directly, but instead a bash script with a source inside
it. This won't work for sourcing environment variables in your shell, so
use --unwrapped when you want to use source.

``--client-logging`` Logs all client output locally on the client to a
file called curlbomb.log

``--client-quiet`` Quiets the output on the client

``--mime-type MIME_TYPE`` The mime-type header to send, by default
"text/plain"

``--disable-knock`` Don't require a X-knock HTTP header from the client.
Normally, curlbombs are one-time-use and meant to be copy-pasted from
terminal to terminal. If you're embedding into a script, you may not
know the knock parameter ahead of time and so this disables that. This
is inherently less secure than the default.

``--version`` Print the curlbomb version

Run subcommand
~~~~~~~~~~~~~~

::

    curlbomb run [-c COMMAND] [--hash SHA256] [--signature FILE_OR_URL [GPG_ID ...]] [SCRIPT]

Runs a shell script on the remote client.

``-c COMMAND`` Set the name of the command that the curlbomb is run with
on the client. By default, this is autodected from the first line of the
script, called the shebang (#!). If none can be detected, and one is not
provided by this setting, the fallback of "bash" is used. Note that
curlbomb will still wrap your script inside of bash, even with ``-c``
specified, so the client command will still show it as running in bash.
The command you specified is put into the wrapped script. See
``--unwrapped`` to change this behaviour.

``--hash SHA256`` Specify the expected SHA-256 hash of the script and
the server will verify that it actually has that hash before the server
starts. This is useful if you are pipeing a script from someplace
outside of your control, like from the network. This prevents the server
from serving a script other than the version you were expecting.

``--signature FILE_OR_URL [GPG_ID ...]`` Specify the file or URL
containing the GPG signature for the script. Optionally specify a list
of GPG key identifiers that are allowed to sign the script. If no
GPG\_ID is specified, any valid signature from your keyring is accepted.
The script will be checked for a valid signature before the server
starts.

``SCRIPT`` The script or other resource to serve via curlbomb. You can
also leave this blank (or specify '-') and the resource will be read
from stdin.

Note that the run subcommand is implied if you are pipeing data to
curlbomb. For instance, this command is assumed that the run command is
desired even if not explicitly used:

::

    echo "./run_server.sh" | curlbomb

Which is equivalent to:

::

    echo "./run_server.sh" | curlbomb run -

Put subcommand
~~~~~~~~~~~~~~

::

    curlbomb put [--exclude=PATTERN] SOURCE [DEST]

Copies file(s) from the local SOURCE path to the remote DEST path. If a
directory is specified, all child paths will be copied recursively.

If DEST path is unspecified, files/directories will be copied to the
working directory of wherever the client was run.

Exclude patterns can be specified like tar(1)

Get subcommand
~~~~~~~~~~~~~~

::

    curlbomb get [--exclude=PATTERN] SOURCE [DEST]

Copies file(s) from the remote SOURCE path to the local DEST path. If a
directory is specified, all child paths will be copied recursively.

If DEST path is unspecified, files/directories will be copied to the
working directory of wherever curlbomb was run.

Exclude patterns can be specified like tar(1)

Ping subcommand
~~~~~~~~~~~~~~~

::

    curlbomb ping [-m MESSAGE] [-r RETURN_CODE] [--return-success]
                  [-c COMMAND] [-n]

Serves an empty body resource for the purposes of pinging the server
when the client has finished some task.

``-m`` sets the message the client will respond with.

``-r`` sets the return code the client will respond with. This is used
as the main curlbomb return code on the server as well. If ``-n`` > 1,
the last non-zero return code received is used instead, defaulting to 0.

``--return-success`` Always return 0, regardless of the return code(s)
received.

``-c COMMAND`` Run this command for each ping received. You can use the
following placeholders to format ping data: {return\_code} and
{message}. {message} is replaced surrounded by quotes, so no need to do
that again in your command.

ssh-copy-id subcommand
~~~~~~~~~~~~~~~~~~~~~~

::

    curlbomb ssh-copy-id IDENTITY

Copies the given OpenSSH identity file (eg. ~/.ssh/id\_rsa.pub) into the
remote ~/.ssh/authorized\_keys file.

Of course OpenSSH comes with it's own ssh-copy-id program, but I've
never really understood the usefulness of it. The idea of using SSH keys
is to not use crappy passwords, right? But the OpenSSH version of
ssh-copy-id requires password authentication (at least temporarily
during the setup process.) So you either have to edit your sshd\_config,
turn on ``PasswordAuthentication``, and restart the service, or you
resign yourself to run an insecure sshd all the time.
``curlbomb ssh-copy-id`` is easier and works in more situations.

Another difference in this version is that you must explicity specify
the identity file, whereas the OpenSSH version does some automatic
determination of which key to install. Especially if you maintain
several ssh identities, being explicit seems the more sane thing to do
than try to save some keystrokes and inevitably install the wrong key on
the server.