curlbomb
========

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

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

::

    bash <(curl -s http://example.com/install.sh)

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

curlbomb reads a file, or from stdin, and then serves it one time to the
first client to retrieve it. 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) required to download the
resource. This command is copied and run in another shell, on some other
computer, to download and run the script in one line.

curlbomb has optional integration with OpenSSH 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.

Install
-------

This script 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

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

Serve a script stored in a file:

::

    curlbomb /path/to/script

This outputs a curl command to run the script on another computer:

::

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

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. (-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 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 also pipe scripts directly into curlbomb:

::

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

Or from shell scripts:

::

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

Or type it interactively:

::

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

The shebang line (#!) is interpreted and automatically changes the
interpreter the client runs:

::

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

Note that the resource curlbomb sends doesn't need to be a script.
Here's a useful command to send a tarball of your private SSH keys to
another client you're setting up:

::

    tar cjh -C $HOME .ssh | curlbomb -c "tar xjv -f"

The -c parameter tells the client what command to run the resource with.
By specifying "tar xj -f" you are telling it to read the resource
directly as a tarball and extract it.

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. 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 local curlbomb HTTP port to example.com:8080. The URL
that curlbomb prints out uses the domain name of the ssh server instead
of the local IP address. The SSH tunnel is left open for as long as
curlbomb remains running. Any user on example.com 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

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 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 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 (ascii-armored) and curlbomb will decrypt it only when
necessary.

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

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

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

::

    usage: curlbomb.py [-h] [-k] [-n N] [-p PORT] [-c CMD] [-d DOMAIN] [-w] [-l]
                       [-q] [-v] [--ssh SSH_FORWARD] [--ssl CERTIFICATE]
                       [--survey] [--unwrapped] [--disable-postback]
                       [--client-logging] [--mime-type MIME_TYPE] [--version]
                       [FILE]

``-k, --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.

``-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.

``-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.

``-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.

``-l, --log-posts`` Log the client output from the curlbomb server.

``-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 (see: man sshd\_config) setting turned on to allow remote
clients to connect to this port.

``--ssl CERTIFICATE`` Run the HTTP server with TLS encryption. Give the
full path to your SSL certificate, optionally PGP (ascii-armored)
encrypted. The file should contain the entire certificate chain,
including the CA certificate, if any.

``--survey`` Only print the curl (or wget) command. Don't redirect to a
shell command. Useful for testing out 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 --disable-postback

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. --disable-postback prevents
the command from being piped back to the server (as source doesn't have
any output, and strangely fails to do it's job when you do pipe it
somewhere else.)

``--disable-postback`` Disables sending client output to the server.
Note that --log-posts will have no effect with this enabled.

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

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

``--version`` Print the curlbomb version

``FILE`` 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.
