Tailor Intrusion Protection for Your Network Assets

This chapter provides an insight into Secure Firewall recommended rules and generating and applying Secure Firewall recommended rules.

Snort 3 Rule Changes in LSP Updates

During regular Snort 3 Lightweight Security Package (LSP) updates, an existing system-defined intrusion rule may be replaced with a new intrusion rule. There could be possibilities of a single rule being replaced with multiple rules, or multiple rules being replaced with a single rule. This occurs when better detection is possible for which rules are combined or expanded. For better management, some existing system-defined rules may also be removed as a part of the LSP update.

To get notifications for changes to any overridden system-defined rules during LSP updates, ensure that the Retain user overrides for deleted Snort 3 rules check box is checked.

To navigate to the Retain user overrides for deleted Snort 3 rules check box, click Cog (cog icon), and then choose Configuration > Intrusion Policy Preferences.

By default this check box is checked. When this check box is checked, the system retains the rule overrides in the new replacement rules that are added as a part of the LSP update. The notifications are shown in the Tasks tab under the Notifications icon that is located next to Cog (cog icon).

Overview of Secure Firewall Recommended Rules

You can use intrusion rule recommendations to target vulnerabilities associated with host assets detected in the network. For example, operating systems, servers, and client application protocols. This allows you to tailor your intrusion policy to the specific needs of your monitored network.

The system makes an individual set of recommendations for each intrusion policy. It typically recommends rule state changes for standard text rules and shared object rules. However, it can also recommend changes for inspector and decoder rules.

When you generate rule state recommendations, you can use the default settings or configure advanced settings. Advanced settings allow you to:

  • Redefine which hosts on your network the system monitors for vulnerabilities

  • Influence which rules the system recommends based on rule overhead

  • Specify whether to generate recommendations to disable rules

You can also choose to use the recommendations immediately or review the recommendations (and affected rules) before accepting them.

Choosing to use recommended rule states adds a read-only Secure Firewall Recommendations layer to your intrusion policy, and subsequently choosing not to use recommended rule states removes the layer.

You can schedule a task to generate recommendations automatically based on the most recently saved configuration settings in your intrusion policy.

The system does not change rule states that you set manually such as:

  • Manually setting the states of specified rules before you generate recommendations prevents the system from modifying the states of those rules in the future.

  • Manually setting the states of specified rules after you generate recommendations overrides the recommended states of those rules.


    Tip

    The intrusion policy report can include a list of rules with rule states that differ from the recommended state.

While displaying the recommendation-filtered Rules page, or after accessing the Rules page directly from the navigation panel or the Policy Information page, you can manually set rule states, sort rules, and take any of the other actions available on the Rules page, such as suppressing rules, setting rule thresholds, and so on.


Note

The Cisco Talos Intelligence Group (Talos) determines the appropriate state of each rule in the system-provided policies. If you use a system-provided policy as your base policy, and you allow the system to set your rules to the Secure Firewall recommended rule state, the rules in your intrusion policy match the settings recommended for your network assets.

Prerequisites for Network Analysis and Intrusion Policies

To allow the Snort inspection engine to process traffic for intrusion and malware analysis, you must have the IPS license enabled for the Threat Defense device.

You must be an Admin user to manage network analysis, intrusion policies, and perform migration tasks.

Generate New Secure Firewall Recommendations in Snort 3

Generate the Secure Firewall recommendations for the intrusion policy and then follow the steps that are listed here to create new recommended rule settings in Snort 3. Rule overheads are interpreted as security levels based on the threshold policies selected by you in Snort 3. Recommended action is based on the selected security level and if it is higher than the base policy, then the recommendation is not just limited to generating the events.

Prior to setting the Secure Firewall recommendations you should ask which of the three points listed below closely matches the goal:

  • Increased Protection —Enable additional rules based on vulnerabilities found in the host database and do not automatically disable any rules. This will likely result in a larger rule set.

  • Focused Protection—Enable additional rules and disable existing rules based on vulnerabilities found in the host database. This can increase or decrease the number of rules depending on vulnerabilities discovered.

  • Higher Efficiency—Use the currently enabled rule set and disable any rules for vulnerabilities not found in the host database. This will likely result in a smaller enabled rule set.

Based on the response, the recommendation actions are as follows:

  • Set recommendations to the next highest security level, and uncheck the disable rules.

  • Set recommendations to the next highest security level, and check the disable rules.

  • Set recommendations to the current security level, and check the disable rules.

Before you begin

Secure Firewall recommendations have the following requirements:

  • Ensure that hosts are present in the system to generate recommendations.

  • Protected networks configured for recommendations should map to the hosts present in the system

Procedure

Step 1

Choose Policies > Intrusion.

Step 2

Click the Snort 3 Version button of the intrusion policy.

Step 3

Click the Recommendations (Not in Use) layer to configure the rule recommendations. Click Start.

In the Secure Firewall Rule Recommendations window you can set the following:

  • Security Level: Click to select the security level. Optionally, you can check the Accept Recommendation to Disable Rules checkbox to disable rules that are not enabled at the input security level and in protected networks. Only enable this option if you need to trim your rule set due to a high number of alerts or to improve inspection performance. The security levels are:

    • Security level 1: Connectivity Over Security

      No Impact—No new rules are enabled and no existing rules are disabled. To increase the protection, select a higher security level.

      Lower Security (checkbox is checked)—All rules are disabled except for the rules in the Connectivity Over Security ruleset that match potential vulnerabilities on discovered hosts. It is recommended instead to adjust the Base Policy.

    • Security level 2: Balanced Security Over Connectivity

      No Impact—No new rules are enabled and no existing rules are disabled. To increase the protection, select a higher security level.

      Higher Efficiency(checkbox is checked)—Keeps existing rules that match potential vulnerabilities on discovered hosts and disables rules for vulnerabilities not found on the network.

    • Security level 3: Security Over Connectivity

      Increased Security—Enables additional rules that match potential vulnerabilities on discovered hosts based on the Maximum Detection ruleset.

      Focused Security(checkbox is checked)—Enables additional rules that match vulnerabilities on discovered hosts based on the Security Over Connectivity ruleset, while disabling existing rules that do not match potential vulnerabilities on discovered hosts.

    • Security level 4 : Maximum Detection

      Increased Security—Enables additional rules that match potential vulnerabilities on discovered hosts based on the Security Over Connectivity ruleset.

      Focused Security (checkbox is checked)—Enables additional rules that match vulnerabilities on discovered hosts based on the Maximum Detection ruleset, while disabling existing rules that do not match potential vulnerabilities on discovered hosts.

      Note

       

      Maximum Detection enables a very high number of rules and may impact performance. We recommend you to review and test this setting before deploying into a production environment.

  • Protected Networks: Specifies the monitored networks or individual hosts to examine for recommendations. You can select one or more system or custom defined network objects from the drop-down list. By default, any IPv4 or IPv6 networks are selected, if no selection is done.

    Important

     

    The Secure Firewall Rule Recommendations depend on network discovery. Protected Networks apply to any hosts discovered within the ranges configured in your Network Discovery policy. For more information, see the chapter Network Discovery Policies in the Cisco Secure Firewall Management Center Device Configuration guide.

    Click the Add + button to create a new network object of type Host or Network and click Save.

Step 4

Generate and apply recommendations:

  • Generate: Generates the recommendations for an intrusion policy. This action lists the rules under Recommended Rules (Not in use).

  • Generate and Apply: Generates and applies the recommendations for an intrusion policy. This action lists the rules under Recommended Rules (In use).

Recommendations are generated successfully. A new recommendation tab appears with all the recommended rules with their corresponding recommended actions. Rule action preset filters are also available for this tab, in addition with new recommendations.

Step 5

You can verify the recommendations and then choose to apply them accordingly:

  • Accept—Applies the previously generated recommendations for an Intrusion policy.

  • Refresh—Regenerates and updates the rule recommendations for an Intrusion policy.

  • Edit—It opens the Recommendations dialog box, you can provide the recommendation input values and then generate the recommendations.

  • Remove All—Revert or remove the applied recommended rules from the policy and also removes the recommendation tab.

Under All Rules, there is a Recommended Rules section which displays the recommended rules.

Note

 

Final action for an Intrusion rule is applied based on the rule action priority order and following is the rule action priority order:

Rule Override > Generated Recommendations > Group Override > Base​ Policy Default Action

For enabled recommendations, management center considers the current state: group overrides, base policy, and recommendation configurations and priority order of actions is:

pass > block > reject > drop > rewrite > alert

What to do next

Deploy configuration changes; see Deploy Configuration Changes.