SSL Inbound Inspection
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SSL Inbound Inspection

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SSL Inbound Inspection

SSL Inbound Inspection protects internal servers from threats posed by SSL/TLS traffic originating from an external server or the Internet.
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 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 internal 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 generates 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, unless the certificate and private key is stored on an HSM. The firewall validates that the certificate sent by the targeted server during the SSL/TLS handshake matches a certificate in your Decryption policy rule. If there is a match, the firewall forwards the server's certificate to the client requesting server access and establishes a secure connection.
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.
Multiple Certificate Support
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.
SSL Inbound Inspection does not support session resumption.
When you configure SSL Inbound Inspection, the proxied traffic does not support DSCP code points or QoS.
To protect internal servers, follow the steps to configure SSL Inbound Inspection policy rules.