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A personal HTTP server for serving one-time-use shell scripts

Project description

A personal HTTP 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.

This script is an HTTP server that will serve that script to a client exactly once and then quit. Yea, you could just use “python -m http.server”, really this is just a bit more than that.

Install

This script can be installed from the Arch User Repository (AUR):

pacaur -S curlbomb

Or from the Python Package Index (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:

bash <(curl http://10.13.37.133:47601 -H "X-knock: c19fed96a78844b982053448e44060f9")

The client must pass a X-knock HTTP header by default. This is for two reasons:

  • It adds a factor of authentication. Requests without the knock are denied.

  • It prevents mistakes as the knock parameter is randomly generated each time curlbomb is run.

You can disable the knock requirement with the -k option.

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

The shebang line (#!) is interpreted and automatically changes the curlbomb command:

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

Which outputs the following curlbomb, tailored for Python:

/usr/bin/env python3 <(curl http://10.13.37.133:55298 -H "X-knock: 3b4bc96e29754238a30c286d1c8173c7")

You can use -c to specify your own command if the shebang line is missing, or misidentified. “bash” is always used as a fallback.

If your client doesn’t have curl installed, you can switch to wget with -w:

$ echo "apt-get install curl" | curlbomb -w
Client command:

  bash <(wget -q -O - http://10.13.37.133:57670 --header="X-knock: 5e5568bf44624e70a7490783acee150d")

By default, curlbomb serves from the local IP address. 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 emacs-nox" | 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. This 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. If you want anyone in the world to be able to fetch 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 SSL with –ssl:

echo "export PASSWORD=hunter2" | curlbomb -c source --ssl /path/to/cert.pem

In the above example we are passing a bit of secure information, a password. curlbomb normally prevents access with a knock paramter, but the knock itself might be spied on through traffic analysis. Using SSL makes sure this doesn’t happen. To prevent having to store the SSL certificate in plain text on your local machine, the file may be optionally PGP encrypted in an ascii-armored file. This will be automatically decrypted if you are running a gpg-agent.

Command Line Args

usage: curlbomb [-h] [-k] [-n NUM_GETS] [-p PORT] [-q] [-c COMMAND] [-w]
                [--ssh SSH_FORWARD] [--ssl CERTIFICATE]
                [--mime-type MIME_TYPE] [--survey]
                [FILE]

-k 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 NUM_GETS The maximum number of times the script may be fetched by clients, defaults 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.

-p PORT The local TCP number to use

-q Be quiet. Don’t print the curlbomb.

-c COMMAND Force the curlbomb shell command. 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, the fallback of “bash” is used.

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

-w Print wget syntax rather than curl syntax. Useful in the case where the client doesn’t have curl installed.

--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].

--ssl CERTIFICATE Full server to client http encryption using SSL. Give the full path to your SSL certificate, optionally PGP (ascii-armored) encrypted.

--mime-type MIME_TYPE The mime-type header to send, by default “text/plain”

FILE The script or other resource to serve via curlbomb. You can also not specify this and the resource will be read from stdin.

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