Identify Security Policy Rules with Unused Applications

Policy Optimizer finds Security policy rules that specify applications not seen on your network so you can remove the unused apps to reduce the attack surface.
If you have application-based Security policy rules that allow a large number of applications, you can remove unused applications (applications never seen on the rules) to tighten those rules so that they only allow applications actually seen in traffic that matches the rule. Identifying and removing unused applications from Security policy rules is a best practice that strengthens your security posture by reducing the attack surface.
  1. Identify Security policy rules that have unused applications.
    Policies
    Security
    Policy Optimizer
    Unused Apps
    displays all application-based rules that are configured with applications that have not matched (been seen on) the rule. This means that these rules allow applications that you may not use in your network (or that another rule shadows the rule, so traffic that you expect to match the rule matches an earlier rule in the rulebase).
    The number of
    Apps Allowed
    and
    Apps Seen
    are updated approximately every hour, so if you configure applications on a rule and don’t see as many
    Apps Allowed
    as you expect, check again after about an hour. Depending on the firewall’s load, it may take longer than one hour for these fields to update.
  2. Prioritize which rules with unused applications to modify first.
    Policies
    Security
    Policy Optimizer
    Unused Apps
    enables you to sort rules without affecting their order in the rulebase and provides other information that helps you prioritize rules to clean up based on your business goals and risk tolerance.
    • The difference between
      Apps Allowed
      (the number of applications on the allow list) and
      Apps Seen
      (the number of allowed applications actually seen on the rule) shows how many applications are configured on each rule but not actually seen on the rule, which indicates to what extent the rule is over-provisioned. Click
      Apps Allowed
      to sort by the number of applications allowed in a rule and click
      Apps Seen
      to sort by the number of applications actually seen on a rule.
    • Days with No New Apps
      (click to sort) shows you the number of days since the last time a new application hit the rule. This indicates how likely it is that the rule is mature and won’t see any applications that haven’t already been seen. The longer the
      Days with No New Apps
      , the less likely that new applications will hit the rule and the more likely that you know all the applications the rule allows.
    • Created
      and
      Modified
      dates also help determine whether a rule has matured enough to understand whether applications not seen on the rule may be seen at a later date or if the rule has seen all the applications expected to hit the rule. The longer the time since a rule was
      Modified
      , the more likely the rule is mature. (If
      Created
      and
      Modified
      are the same, the rule hasn’t been modified.)
    • Hit Count
      —Displays rules with the most matches over a selected time frame. You can exclude rules for which you reset the hit counter and specify the exclusion time period in days. Excluding rules with recently reset hit counters prevents misconceptions about rules that show fewer hits than you expect because you didn’t know the counter was reset.
      You can also use
      Hit Count
      to View Policy Rule Usage.
    You can also click
    Traffic (Bytes, 30 days)
    to sort by the amount of traffic a rule has seen over the last 30 days. Use this information to prioritize which rules to modify first. For example, you can prioritize rules with the largest difference between
    Apps Allowed
    and
    Apps Seen
    and that also have the most
    Days with No New Apps
    , because those rules have the greatest number of unused applications and are the most mature.
  3. Review the
    Apps Seen
    on the rule.
    On
    Unused Apps
    , click
    Compare
    or the number in the
    Apps Seen
    column to open
    Applications & Usage
    , which shows the applications configured on the rule (
    Apps on Rule
    ) and the
    Apps Seen
    on the rule.
    • The number next to
      Apps Seen
      (10 in this example) is the number of applications that matched the rule. Keep in mind that it takes at least one hour for the firewall to update
      Apps Seen
      .
    • The number next to
      Apps on Rule
      (35 in this example) is how many applications are configured on the rule, which is calculated by counting each application in a container app (but not the container app itself—if you configure a container app on the rule, the rule allows the container app’s individual applications). Because the
      Applications
      list shows only the applications you configure manually on the rule, when you configure a container app on a rule,
      Applications
      only shows the container app, not all of the individual applications in the container (unless you also manually configure the individual applications on the rule). For this reason, the number of
      Apps on Rule
      may not be the same as the number of applications you see in the
      Applications
      list.
    • Click the number next to
      Apps on Rule
      to see all of the individual applications on the rule.
      This example rule has 10
      Apps Seen
      (applications that matched the rule) but allows 35
      Apps on Rule
      . The
      facebook
      container app is configured on the rule and the rule sees traffic from the individual applications facebook-base, facebook-chat, and facebook-video (
      Apps Seen
      ). When you click the
      Apps on Rule
      number, the
      Apps on Rule
      dialog displays the individual applications allowed, but not the container app itself.
      You cannot add or delete applications from the pop-up dialog.
    Compare the
    Apps Seen
    on the rule to the
    Apps on Rule
    . If an application on the rule isn’t used (you don’t see the application or you don’t see applications in an allowed container in
    Apps Seen
    ), consider removing the application from the rule to reduce the attack surface. Take into account periodically used applications, such as for quarterly or annual events, which may look unused if you don’t examine a long enough time frame.
    Timeframe
    enables you to select the time frame for the
    Apps Seen
    on the rule. Select
    Anytime
    to see every application seen over the life of the rule. Depending on the
    Created
    or
    Modified
    date in the
    No App Specified
    dialog and the time between periodic events, the rule may not have been on the firewall long enough to see all periodically used applications.
  4. Remove unused applications from the rule.
    Delete
    (or
    Add
    ) applications in
    Apps on Rule
    to remove (or add) applications manually, or
    Match Usage
    to add the
    Apps Seen
    on the rule and delete applications for which no matching traffic has been seen on the rule with one click.
    To remove applications from the rule manually, select applications from
    Apps on Rule
    and
    Delete
    them. Ensure that none of the applications are required for periodic events before you remove them from the rule. (You can also add or delete applications on the Security policy rule’s
    Application
    tab.)
    Match Usage
    moves the
    Apps Seen
    on the rule to
    Apps on Rule
    and removes all unused applications from the rule.
    You can clone rules from
    Policies
    Security
    and from
    No App Specified
    to Migrate Port-Based to App-ID Based Security Policy Rules. You can’t clone a rule starting from
    Unused Apps
    .
  5. Commit
    the configuration.
  6. Monitor updated rules and listen to user feedback to ensure that updated rules allow the applications you want to allow and don’t inadvertently block periodically used applications.
    The number of
    Apps Allowed
    and
    Apps Seen
    are updated approximately every hour. After you remove all of the unused applications from a rule, the rule remains listed in
    Policies
    Security
    Policy Optimzer
    Unused Apps
    until the firewall updates the display. When the firewall updates the display and the number of
    Apps Allowed
    is the same as the number of
    Apps Seen
    , the rule no longer displays in the
    Unused Apps
    screen. However, depending on the firewall’s load, it may take longer than one hour for these fields to update.

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