Pablo Guides

## Kali Linux Tool: cntlm$

### Introduction to cntlm$

In the realm of network security, the ability to navigate and configure proxy authentication is essential for penetration testers and security professionals. Among the tools available on Kali Linux, **cntlm** stands out as a robust solution for managing authentication with NTLM (NT LAN Manager) proxies. In this section, we will cover how to install, configure, and effectively use cntlm$ in various scenarios.

### What is cntlm?

**Cntlm** is a proxy that is designed to work as an authentication relay for NTLM, which is a challenge-response authentication protocol used by Microsoft. It serves as a bridge between your local application and a Microsoft ISA proxy server, allowing you to authenticate against the proxy without directly exposing your password to the application.

### Installation of cntlm on Kali Linux

To install cntlm on your Kali Linux system, follow these steps:

1. **Open Terminal**: Access your terminal window.

2. **Update Your Package List**: It is crucial to ensure that your package list is up to date. Execute the following command:

   sudo apt update

 

3. **Install cntlm**: You can install cntlm using the following command:

   sudo apt install cntlm

 

4. **Verify Installation**: After installation, confirm that cntlm is installed correctly:

   cntlm -h

 

### Configuration of cntlm

Once installed, you need to configure cntlm to work correctly with your proxy settings:

1. **Edit the Configuration File**: The main configuration file is typically located at `/etc/cntlm.conf`. Open it in a text editor:

   sudo nano /etc/cntlm.conf

 

2. **Basic Configuration Settings**:
– **Set your Username**: Specify your NTLM username.
– **Set your Domain**: Specify your domain name.
– **Set your Password**: You can leave it blank for now; we will generate a hashed version soon.
– **Specify the Proxy**: Indicate the upstream proxy you will connect to.

Example snippet of the configuration file:
[/dm_code_snippet]plaintext
Username your_username
Domain your_domain
Password your_password
Proxy http://your_proxy:8080
NoProxy localhost, 127.0.0.1
[/dm_code_snippet]

3. **Generate Hashed Password**: You should not store your password in plain text. Instead, you can generate a hashed password. Run the following command:

   cntlm -c /etc/cntlm.conf -H

 

Replace the `Password` field in your configuration file with the generated hash.

4. **Start the cntlm Service**:

   sudo systemctl start cntlm

 

5. **Enable cntlm at Boot**:

   sudo systemctl enable cntlm

 

### Step-by-Step Usage of cntlm

Once cntlm is installed and configured, you can use it in various contexts. Below, we will explore some practical applications.

#### Basic Command-Line Proxy Usage

You can use cntlm as a proxy for tools that support the HTTP proxy setting. Here’s how you’d typically use it:

1. **Set Environment Variables**:
If you are using command-line tools like `curl` or `wget`, you will need to set the HTTP proxy environment variables. This ensures that all requests are routed through cntlm.

   export http_proxy=http://localhost:3128

   export https_proxy=http://localhost:3128

 

2. **Using curl**:
You can test your connection to the internet through the proxy:

   curl -I http://www.example.com

 

3. **Using wget**:
Similarly, with `wget`, you can download files:

   wget http://www.example.com/file.zip

 

### Real-World Use Cases

#### 1. Bypassing Corporate Firewalls

In many corporate environments, access to external websites is restricted through NTLM proxies. cntlm can help pentesters access these sites without modifying their local settings.

#### 2. API Testing

When testing web applications, you may have to interact with APIs that are behind NTLM proxies. Using cntlm, you can authenticate and send requests seamlessly.

#### 3. Browser Configuration

If you want to use cntlm with browsers like Firefox or Chrome, you can set the proxy settings in the browser to use `localhost:3128` as the proxy address.

### Detailed Technical Explanations

#### How cntlm Works

Cntlm operates by intercepting requests from your applications, authenticating them against the NTLM proxy, and then forwarding the requests to the intended destinations. This process involves several steps:

1. **Challenge-Response Authentication**: When a request is made to a secure resource, the NTLM server sends a challenge to the client, which cntlm responds to using the authenticated credentials stored in the configuration file.

2. **Session Management**: Cntlm maintains session states for each authenticated user, allowing multiple concurrent connections.

3. **Flexibility**: Cntlm supports various authentication types (NTLMv1, NTLMv2, etc.), making it versatile for different environments.

#### Security Considerations

While cntlm provides a secure way to handle NTLM authentication, it is critical to keep the configuration file secure. Ensure that only authorized users have access to `/etc/cntlm.conf`.

Use the following command to restrict access:
"`bash
sudo chmod 600 /etc/cntlm.conf
"`

### External References

For further reading and to deepen your understanding, consider the following resources:

– [cntlm Official Documentation](http://cntlm.sourceforge.net/)
– [Kali Linux Documentation](https://www.kali.org/docs/)
– [NTLM Explained](https://docs.microsoft.com/en-us/windows/win32/secmgmt/ntlm)

### Code Examples

Here are some code snippets for configuration and basic usage:

#### Configuration Example
"`plaintext
# /etc/cntlm.conf
Username your_username
Domain your_domain
Password your_generated_hash
Proxy http://your_proxy:8080
NoProxy localhost, 127.0.0.1
"`

#### Command-Line Usage Example
"`bash
# Setting up proxy for curl
export http_proxy=http://localhost:3128
curl -I http://www.example.com
"`

"`bash
# Setting up proxy for wget
export https_proxy=http://localhost:3128
wget http://www.example.com/file.zip
"`

In conclusion, cntlm is an indispensable tool for professionals dealing with NTLM proxies. By mastering its installation, configuration, and usage, you will enhance your ability to conduct thorough penetration tests while navigating complex network environments.

—

Made by pablo rotem / פבלו רותם