How to Configure Squid Proxy Server for SSL Bumping

How to Configure Squid Proxy Server for SSL Bumping

One of the ways to ensure secure communication is through the use of Secure Sockets Layer (SSL) or Transport Layer Security (TLS), which encrypts the data between the client and the server. However, this can pose a challenge for proxy servers like Squid, as they cannot view or modify the encrypted content. This is where SSL Bumping comes in. SSL Bumping allows the Squid proxy server to view and modify the encrypted content for various purposes like content filtering, data loss prevention, and compliance.

In this tutorial, we will guide you through the process of configuring Squid Proxy Server for SSL Bumping on CentOS. This will allow your Squid server to act as a man-in-the-middle for SSL encrypted traffic, giving you greater control and visibility over the data that passes through your server.

Please note that SSL Bumping should be used responsibly due to the privacy implications. It’s important to inform users that their encrypted traffic is being intercepted and to only use SSL Bumping for legitimate purposes.

Before we start, make sure you have Squid installed on your CentOS server. If not, you can refer to our previous tutorial on how to install Squid Proxy Server.

Step 1: Generating SSL Certificates

The first step in configuring SSL Bumping is to generate SSL certificates that will be used by Squid to intercept and decrypt SSL traffic.

openssl req -new -newkey rsa:2048 -days 365 -nodes -x509 -keyout /etc/squid/ssl_cert/myCA.pem -out /etc/squid/ssl_cert/myCA.pem

This command will generate a new RSA private key and a self-signed certificate in the /etc/squid/ssl_cert/ directory. You will be asked to enter some information for the certificate, such as the country name, state or province name, etc.

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Step 2: Configuring Squid for SSL Bumping

Next, we need to configure Squid to use the SSL certificates for SSL Bumping. Open the Squid configuration file in a text editor:

nano /etc/squid/squid.conf

Add the following lines to the configuration file:

http_port 3128 ssl-bump generate-host-certificates=on dynamic_cert_mem_cache_size=4MB cert=/etc/squid/ssl_cert/myCA.pem
sslcrtd_program /usr/lib64/squid/security_file_certgen -s /var/lib/ssl_db -M 4MB
ssl_bump peek all
ssl_bump splice all

These lines tell Squid to listen on port 3128 and use the SSL certificates for SSL Bumping. The ‘sslcrtd_program’ line specifies the program to use for generating SSL certificates on the fly. The ‘ssl_bump peek all’ line tells Squid to peek at the beginning of the SSL handshake, and the ‘ssl_bump splice all’ line tells Squid to splice the connection (i.e., act as a pass-through) after peeking.

Step 3: Initializing the SSL Certificate Storage

Before we can start Squid, we need to initialize the SSL certificate storage:

/usr/lib64/squid/security_file_certgen -c -s /var/lib/ssl_db -M 4MB
chown -R squid:squid /var/lib/ssl_db

The first command creates the SSL certificate storage, and the second command changes the ownership of the storage directory to the ‘squid’ user.

Step 4: Starting Squid

Now that we have configured Squid for SSL Bumping, we can start the Squid service:

systemctl start squid

To ensure that Squid starts automatically at boot, enable the Squid service:

systemctl enable squid

Step 5: Testing the Configuration

To test if SSL Bumping is working correctly, you can use a web browser to access an HTTPS website through the Squid proxy server. If the website loads correctly, this means that SSL Bumping is working.

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Conclusion

In this tutorial, we have shown you how to configure Squid Proxy Server for SSL Bumping on CentOS. This allows your Squid server to act as a man-in-the-middle for SSL encrypted traffic, giving you greater control and visibility over the data that passes through your server.

Remember, SSL Bumping should be used responsibly due to the privacy implications. Always inform users that their encrypted traffic is being intercepted and only use SSL Bumping for legitimate purposes.

For more information about Squid and its features, you can visit our Squid Guide.

If you have any questions or run into any issues, feel free to leave a comment below.

Commands Mentioned:

  • openssl req -new -newkey rsa:2048 -days 365 -nodes -x509 -keyout /etc/squid/ssl_cert/myCA.pem -out /etc/squid/ssl_cert/myCA.pem – Generates a new RSA private key and a self-signed certificate.
  • nano /etc/squid/squid.conf – Opens the Squid configuration file in a text editor.
  • /usr/lib64/squid/security_file_certgen -c -s /var/lib/ssl_db -M 4MB – Creates the SSL certificate storage.
  • chown -R squid:squid /var/lib/ssl_db – Changes the ownership of the storage directory to the ‘squid’ user.
  • systemctl start squid – Starts the Squid service.
  • systemctl enable squid – Enables the Squid service to start on boot.
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FAQ

  1. What is SSL Bumping?

    SSL Bumping is a technique used by Squid Proxy Server to view and modify SSL encrypted traffic. It allows the Squid server to act as a man-in-the-middle for SSL encrypted traffic, giving greater control and visibility over the data that passes through the server.

  2. Why do I need SSL Bumping?

    SSL Bumping is needed when you want to inspect or modify the content of SSL encrypted traffic that passes through your Squid Proxy Server. This can be useful for various purposes like content filtering, data loss prevention, and compliance.

  3. Is SSL Bumping secure?

    SSL Bumping itself does not compromise the security of the SSL encrypted traffic. However, it should be used responsibly due to the privacy implications. It’s important to inform users that their encrypted traffic is being intercepted and to only use SSL Bumping for legitimate purposes.

  4. Can I use SSL Bumping on other operating systems?

    Yes, while this tutorial focuses on CentOS, the process of setting up SSL Bumping with Squid is similar on other Linux distributions. The main difference would be the package installation process and the location of the configuration files.

  5. What other features does Squid offer?

    Squid offers a wide range of features beyond SSL Bumping. It can be used for caching web content, filtering web traffic, load balancing, and more.

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