SSL Inbound Inspection
Focus
Focus

SSL Inbound Inspection

Table of Contents

SSL Inbound Inspection

SSL Inbound Inspection decryption decrypts inbound traffic so the firewall can protect against threats in the encrypted traffic destined for your servers.
Use SSL Inbound Inspection to decrypt and inspect inbound SSL/TLS traffic from a client to a targeted network server (any server you have the certificate for and can import it onto the firewall) and block suspicious sessions. For example, suppose a malicious actor wants to exploit a known vulnerability in your web server. Inbound SSL/TLS decryption provides visibility into the traffic, allowing the firewall to respond to the threat proactively.
SSL Inbound Inspection works similarly to SSL Forward Proxy, except that the firewall decrypts inbound traffic to servers instead of decrypting outbound traffic from internal clients. The firewall acts as a man-in-the-middle proxy between the external client and the internal server and must generate a new session key for each secure session. The firewall creates a secure session between the client and the firewall and another secure session between the firewall and the server to decrypt and inspect the traffic.
Because the firewall is a proxy device, SSL Inbound Inspection cannot decrypt some sessions, such as sessions with client authentication or pinned certificates. Being a proxy also means that the firewall does not support High Availability (HA) sync for decrypted SSL sessions.
On the firewall, you must install the certificate and private key for each server for which you want to perform SSL Inbound Inspection. The TLS versions that your web server supports determine how you should install the server certificate and key on the firewall. If your web server supports TLS 1.2 and Rivest, Shamir, Adleman (RSA) or Perfect Forward Secrecy (PFS) key exchange algorithms and your end-entity (leaf) certificate is signed by intermediate certificates, we recommend uploading a certificate chain (a single file) to the firewall. Uploading the chain avoids client-side server certificate authentication issues.
TLS 1.3 removes support for the RSA key exchange algorithm.
The firewall handles TLS 1.3 connections differently than TLS 1.2 connections. During TLS 1.3 handshakes, the firewall sends the client the same certificate or certificate chain that it receives from the server. As a result, uploading the server certificate and private key to the firewall is sufficient if you correctly set up your web server. For example, if your server’s leaf certificate is signed by intermediate certificates, the chain of certificates needs to be installed on the server to avoid client-side server authentication issues.
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, but check performance to ensure that the firewall resources can handle the higher processing load that higher security protocols and algorithms require.
When you configure SSL Inbound Inspection and use a PFS cipher, session resumption is not supported.
When you configure SSL Inbound Inspection, the proxied traffic does not support DSCP code points or QoS.
To protect an internal server, follow the steps to configure SSL Inbound Inspectionpolicy rules.