How to Configure Server DPI-SSL

10/14/2021 710 People found this article helpful 494,088 Views

Description

SonicWall DPI-SSL

Deep Packet Inspection of Secure Socket Layer (DPI-SSL) extends SonicWall’s Deep Packet Inspection technology to allow for the inspection of encrypted HTTPS traffic and other SSL-based traffic. The SSL traffic is decrypted transparently, scanned for threats and then re-encrypted and sent along to its destination if no threats or vulnerabilities are found. DPI-SSL provides additional security, application control, and data leakage prevention for analyzing encrypted HTTPS and other SSL-based traffic.

The following security services and features are capable of utilizing DPI-SSL:

Gateway Anti-Virus
Gateway Anti-Spyware
Intrusion Prevention
Content Filtering
Application Firewall
Packet Capture
Packet Mirror

SERVER DPI-SSL

Server DPI-SSL is one of two deployment scenarios, the other being Client DPI-SSL, used to inspect SSL-based traffic. Server DPI-SSL deployment scenario is typically used to inspect HTTPS traffic when remote clients
connect over the WAN to access content located on the SonicWall security appliance’s LAN (or DMZ).

ServerDPI-SSL is able to decrypt SSL-based traffic in the following manner:

Configure pairing of an internal address object and certificate.
When the appliance detects SSL connections to the address object, it presents the paired certificate and negotiates an SSL connection with the connecting client. This enables the SonicWall to inspect the traffic and, if a threat is detected, to enforce Security Services and Application Firewall policies.

In this deployment scenario the owner of the SonicWall UTM owns the certificates and private keys of the origin content servers. Administrators will have to import the server's original certificate into the UTM appliance and create appropriate server IP address to server certificate mappings in the Server DPI-SSL UI.

Further, the pairing of internal address objects with certificates can be either encrypted or "Cleartext". If the pairing is not defined to be cleartext, then an SSL connection to the server is negotiated. This allows for end-to-end encryption of the connection. If the pairing defines the server to be 'cleartext' then a standard TCP connection is made to the server on the original (post NAT remapping) port.

This article illustrates the procedure to configure Server DPI-SSL in the SonicWall UTM.

Resolution

Resolution for SonicOS 6.5

This release includes significant user interface changes and many new features that are different from the SonicOS 6.2 and earlier firmware. The below resolution is for customers using SonicOS 6.5 firmware.

The following NAT Policy and Access Rule requires to be in place before beginning the confguration process.

Importing the Server Certificate

In order for the SonicWall to be able to act as a re-signing authority, the administrator have to import the Server's certificate along with private key. This would be a PKCS-12 formatted certificate file. Exporting (or creating) a certificate with public and private keys is explained in Exporting the Server Certificate along with Private Key section.

Login to the SonicWall Management interface.
Navigate to Manage | Appliance | Certificates
At the bottom of the page, click on the Import button to open the Import Certificate window.
Select the radio button under Import a local end-user certificate with private key from a PKCS#12 (.p12 or .pfx) encoded file.
Enter a name for the certificate
Enter the password for the certificate under Certificate Management Password
Click on Browse and select the certificate
Click on Import to import the certificate.

Enabling Server DPI-SSL

Navigate to the Manage | Deep Packet Inspection | SSL Client Deployment page.
Select the checkbox under Enable SSL Server Inspection
Click on the Accept button at the top of the page to save the change.

You will be required to restart the SonicWall.

Under SSL Servers, click on the Add button to bring up the Server DPI-SSL window.
In the Address Object/Group pulldown menu, select the address object or group for the server or servers that you want to apply DPI-SSL inspection to.
In the SSL Certificate pulldown menu, select the certificate that will be used to sign the traffic for the server.
Leave the Cleartext box unchecked. More on the Cleartext below.
Click on Add and click on Close to save.

Using the Cleartext option

The cleartext option indicates that the portion of the TCP connection between the UTM appliance and the local server will be in the clear without SSL layer, thus allowing SSL processing to be offloaded from the server by the appliance.

In order for such configuration to work properly, the NAT policy should translated from an SSL port to a non-SSL port. For example, in case of HTTPS traffic being used with SSL offloading, an inbound NATpolicy remapping traffic from port 443 to another port needs to be created in order for things to work properly. A port other than port 80 should be used, because port 80 is used for clear text data inbound to the server.

Exporting or creating a PKCS-12 Formatted Certificate File

As mentioned in the Importing Certificate section, Server DPI-SSL deployment requires the administrator to import the server's certificate with private key. This section illustrates the example of creating and/or exporting a PKCS-12 formatted certificate file (.pfx) using Linux and Windows 2008.

Linux Apache HTTP server

The private key and certificate is located in the following locations: /etc/httpd/conf/ssl.key/server.key and /etc/httpd/conf/ssl.crt/server.crt. With these 2 files available, run the following command:

openssl pkcs12 -export -out out.p12 -inkey server.key -in server.crt

Where out.p12 will become PKCS-12 formatted certificate file and server.key and server.crt are PEM formatted private key and certificate file respectively. After the above command, one would be prompted for the password to
protect/encrypted the file. After the password is chosen, the creation of PKCS-12 formatted certificate file is complete and it can be imported into the UTM appliance.

Windows Server 2008

In Microsoft Windows, the PKCS-12 formatted certificate file can be exported either from Internet Information Services (IIS) Manager under Certificates. The following screenshots show the export process:

How to Test:

Based on the above configuration, the following test website was hosted with links to download files of type exe, zip, pdf etc.

The following logs are displayed when user tries to download any one of the file above because App Control Advanced has been configured to block download of file types exe, zip and pdf.

GAV Block Message and log

Resolution for SonicOS 6.2 and Below

The below resolution is for customers using SonicOS 6.2 and earlier firmware. For firewalls that are generation 6 and newer we suggest to upgrade to the latest general release of SonicOS 6.5 firmware.