Unveiling SSL Inbound Decryption: Strengthening Network Security with Palo Alto Firewall

Introduction

It’s been a busy weekend (it always is with 2 toddlers) but I wanted to build off the blog I did last week on (outbound) SSL decryption. If you’re interested in that one, check it out here. I’ve had a lot of great feedback on that one, so let’s build off of that. Let’s go!

In today's digital landscape, securing sensitive data transmitted over the internet is paramount for organizations. While SSL encryption provides a layer of protection, it can also obscure malicious threats hidden within encrypted traffic. Palo Alto Networks Next-Generation Firewalls (NGFWs) offer a powerful solution to this challenge through SSL inbound decryption. In this blog post, we'll explore SSL inbound decryption on a Palo Alto Firewall, providing step-by-step guidance on how to implement this critical security feature!

Understanding SSL Inbound Decryption

SSL inbound decryption is a process by which encrypted SSL/TLS traffic entering an organization's network is intercepted, decrypted, inspected for threats, and then re-encrypted before reaching its destination. By decrypting inbound SSL traffic, organizations can effectively enforce security policies, detect and prevent threats concealed within encrypted communication, and ensure regulatory compliance without compromising privacy.

Steps to Implement SSL Inbound Decryption on a Palo Alto Firewall

Step 1: Enable SSL Inbound Decryption

1. Log in to the Palo Alto Networks NGFW web interface.

2. Navigate to the "Objects" tab and select "Decryption Profiles."

3. Create a new decryption profile or modify an existing one to enable SSL inbound decryption.

4. Specify the decryption policy settings, including SSL protocol versions, certificate verification options, and decryption exemptions (if needed)

   1. NOTE: When you configure the SSL Protocol Settings Decryption Profile for SSL Inbound Inspection traffic, create separate profiles for servers with different security capabilities. For example, if one set of servers supports only RSA, the SSL Protocol Settings only need to support RSA. However, the SSL Protocol Settings for servers that support PFS should support PFS. Configure SSL Protocol Settings for the highest level of security that the server supports

Step 2: Configure SSL Decryption Policies for Inbound Traffic

1. Navigate to the "Policies" tab and select "Decryption."

2. Create a new decryption policy rule specifically for inbound traffic to define the traffic to be decrypted.

   1. NOTE: Best practice is to configure or select an existing Decryption Profile to block and control various aspects of the decrypted traffic (for example, create a Decryption profile to terminate sessions with unsupported algorithms and unsupported cipher suites).

3. Specify the source zones, addresses, applications, and users for the inbound decryption policy.

4. Set the action to "decrypt" and apply the decryption profile created in the previous step.

Step 3: Manage SSL/TLS Certificates

1. Obtain and import SSL/TLS certificates into the Palo Alto NGFW for SSL inbound decryption.

2. Ensure that the NGFW has the necessary root CA certificates to validate SSL certificates presented by external servers during the decryption process.

   1. NOTE: Palo Alto recommends uploading a certificate chain (a single file) to the firewall if your end-entity (leaf) certificate is signed by one or more intermediate certificates and your web server supports TLS 1.2 and PFS key exchange algorithms. Uploading the chain avoids client-side server certificate authentication issues.

3. Manage certificate revocation lists (CRLs) and Online Certificate Status Protocol (OCSP) responders to verify the validity of SSL certificates.

Step 4: Monitor SSL Inbound Decryption Traffic

1. Utilize the Palo Alto NGFW's monitoring tools to view decrypted inbound traffic logs and analyze SSL decryption events.

2. Monitor SSL inbound decryption performance metrics to ensure optimal firewall performance and identify any issues or anomalies.

3. Send all inbound SSL decrypted traffic to WildFire for analysis

   1. NOTE: Requires a Wildfire license

Conclusion: Enhancing Network Security with SSL Inbound Decryption

SSL inbound decryption on Palo Alto Firewalls empowers organizations to protect against advanced threats concealed within encrypted inbound traffic. By following the steps outlined above, organizations can strengthen their network security posture, mitigate risks, and ensure compliance with regulatory requirements. As cyber threats evolve, SSL inbound decryption remains a critical component of a comprehensive cybersecurity strategy, enabling organizations to stay ahead of emerging threats and safeguard their critical assets effectively.

Does your organization use inbound SSL Decryption? Let me know in the comments!