Certgraph on Kali Linux Tools

Introduction

Kali Linux is one of the most widely used penetration testing distributions, packed with powerful tools designed for cybersecurity professionals. Among its vast toolkit is Certgraph, a tool used for certificate transparency (CT) log analysis, allowing users to enumerate subdomains and gain insights into SSL/TLS certificates. This makes it a valuable asset for reconnaissance and security assessments.

In this blog post, we will delve deep into Certgraph, exploring its functionality, installation, and practical applications. Whether you’re a penetration tester, a security researcher, or someone interested in ethical hacking, this guide will equip you with the knowledge to leverage Certgraph effectively.

What is Certgraph?

Certgraph is a tool that utilizes certificate transparency (CT) logs to map out relationships between domains and subdomains. CT logs are public records of SSL/TLS certificates issued by Certificate Authorities (CAs). By analyzing these logs, Certgraph can help security professionals discover subdomains associated with an organization, which is particularly useful for reconnaissance in penetration testing.

Key Features of Certgraph

• Retrieves SSL/TLS certificate data from public CT logs.
• Maps domain and subdomain relationships.
• Assists in subdomain enumeration for penetration testing.
• Provides structured JSON output for easy integration with other tools.
• Helps security teams monitor SSL/TLS certificates for unauthorized issuance.

Installing Certgraph on Kali Linux

Certgraph is a Python-based tool, and installing it on Kali Linux is relatively straightforward. Follow these steps to get started:

Step 1: Update Your System

Before installing any new tool, it’s always a good practice to update your system to ensure you have the latest packages.

sudo apt update && sudo apt upgrade -y

Step 2: Install Python3 and Pip

Since Certgraph is a Python tool, make sure you have Python3 and pip installed:

sudo apt install python3 python3-pip -y

Step 3: Clone the Certgraph Repository

Next, clone the Certgraph repository from GitHub:

git clone https://github.com/CertGraph/certgraph.git
cd certgraph

Step 4: Install Required Dependencies

Use pip to install the required dependencies:

pip3 install -r requirements.txt

Now, Certgraph should be ready for use on your Kali Linux system.

Using Certgraph for Domain Analysis

Once installed, you can start using Certgraph for domain enumeration and SSL/TLS certificate mapping.

Basic Syntax

Certgraph can be run using the following command format:

python3 certgraph.py --domain example.com

This will query CT logs and return a structured JSON output containing subdomains and certificate information associated with example.com.

Example Output

Running Certgraph on a domain might return results like this:

{
    "domain": "example.com",
    "subdomains": [
        "mail.example.com",
        "vpn.example.com",
        "dev.example.com"
    ],
    "certificates": [
        {
            "issuer": "Let's Encrypt",
            "serial_number": "1234567890",
            "valid_from": "2023-01-01",
            "valid_to": "2023-04-01"
        }
    ]
}

This information helps penetration testers and security researchers identify potential attack surfaces by discovering hidden subdomains.

Advanced Usage and Options

Filtering by Issuer

To retrieve certificates only from a specific Certificate Authority (CA), use the --issuer flag:

python3 certgraph.py --domain example.com --issuer "Let's Encrypt"

Output Formatting

By default, Certgraph outputs JSON. However, you can format the results for easier readability using third-party tools like jq:

python3 certgraph.py --domain example.com | jq .

Saving Results to a File

You can save results to a file for further analysis:

python3 certgraph.py --domain example.com > results.json

Integrating Certgraph with Other Kali Linux Tools

One of the best things about Certgraph is its ability to integrate with other reconnaissance tools in Kali Linux. Here are a few ways to extend its functionality:

Combining with subfinder

subfinder is another subdomain enumeration tool that can complement Certgraph’s findings.

subfinder -d example.com | certgraph.py --domain

Using with amass

amass is a powerful reconnaissance tool that also uses CT logs. You can compare Certgraph’s results with Amass to ensure thorough enumeration.

amass enum -d example.com
python3 certgraph.py --domain example.com

Feeding Data into nmap

Once you have a list of subdomains, you can perform network scanning using nmap:

nmap -sV -p 80,443 -iL subdomains.txt

Practical Use Cases for Certgraph

1. Bug Bounty Hunting

Certgraph is a great tool for bug bounty hunters looking to identify subdomains belonging to a target organization. Hidden subdomains might expose vulnerable services.

2. Security Monitoring

Organizations can use Certgraph to monitor CT logs and detect unauthorized SSL/TLS certificate issuance, preventing potential phishing attacks.

3. Penetration Testing

During a penetration test, identifying subdomains and mapping SSL/TLS certificates can reveal weak spots in an organization’s security infrastructure.

4. Red Team Operations

Red teams can use Certgraph to gather intelligence on target organizations and build attack strategies based on discovered domains.

Limitations and Considerations

While Certgraph is a powerful tool, it does have some limitations:

• Dependence on CT Logs: It can only retrieve information that is publicly logged in CT logs, meaning some subdomains may not be visible.
• False Positives: Sometimes, subdomains listed in CT logs may no longer be in use.
• Legal Considerations: Always ensure you have permission before using Certgraph on domains you don’t own.

Conclusion

Certgraph is an essential tool for anyone involved in cybersecurity, penetration testing, or bug bounty hunting. Its ability to analyze SSL/TLS certificate data and map out domain relationships makes it a valuable asset for reconnaissance and security monitoring. By integrating Certgraph with other tools in Kali Linux, you can enhance your security assessments and improve your overall cybersecurity posture.

Whether you’re a beginner or an experienced security professional, experimenting with Certgraph on Kali Linux is a great way to gain deeper insights into certificate transparency and domain enumeration. Try it out, explore its features, and incorporate it into your cybersecurity workflow!

Have you used Certgraph in your security assessments? Share your experiences in the comments below!