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.
- Identify Security policy rules that have unused applications.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).PoliciesSecurityPolicy OptimizerUnused AppsThe number ofApps AllowedandApps Seenare updated approximately every hour, so if you configure applications on a rule and don’t see as manyApps Allowedas 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.
- Prioritize which rules with unused applications to modify first.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.PoliciesSecurityPolicy OptimizerUnused Apps
You can also clickTraffic (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 betweenApps AllowedandApps Seenand that also have the mostDays with No New Apps, because those rules have the greatest number of unused applications and are the most mature.
- The difference betweenApps Allowed(the number of applications on the allow list) andApps 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. ClickApps Allowedto sort by the number of applications allowed in a rule and clickApps Seento 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 theDays 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.
- CreatedandModifieddates 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 wasModified, the more likely the rule is mature. (IfCreatedandModifiedare 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.
- Review theApps Seenon the rule.OnUnused Apps, clickCompareor the number in theApps Seencolumn to openApplications & Usage, which shows the applications configured on the rule (Apps on Rule) and theApps Seenon the rule.
Compare theApps Seenon the rule to theApps 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 inApps 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.Timeframeenables you to select the time frame for theApps Seenon the rule. SelectAnytimeto see every application seen over the life of the rule. Depending on theCreatedorModifieddate in theNo App Specifieddialog and the time between periodic events, the rule may not have been on the firewall long enough to see all periodically used applications.
- The number next toApps 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 updateApps Seen.
- The number next toApps 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 theApplicationslist shows only the applications you configure manually on the rule, when you configure a container app on a rule,Applicationsonly 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 ofApps on Rulemay not be the same as the number of applications you see in theApplicationslist.
- Click the number next toApps on Ruleto see all of the individual applications on the rule.This example rule has 10Apps Seen(applications that matched the rule) but allows 35Apps on Rule. TheApps Seen). When you click theApps on Rulenumber, theApps on Ruledialog displays the individual applications allowed, but not the container app itself.You cannot add or delete applications from the pop-up dialog.
- Remove unused applications from the rule.Delete(orAdd) applications inApps on Ruleto remove (or add) applications manually, orMatch Usageto add theApps Seenon 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 fromApps on RuleandDeletethem. 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’sApplicationtab.)Match Usagemoves theApps Seenon the rule toApps on Ruleand removes all unused applications from the rule.
- Committhe configuration.
- 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 ofApps AllowedandApps Seenare updated approximately every hour. After you remove all of the unused applications from a rule, the rule remains listed inuntil the firewall updates the display. When the firewall updates the display and the number ofPoliciesSecurityPolicy OptimzerUnused AppsApps Allowedis the same as the number ofApps Seen, the rule no longer displays in theUnused Appsscreen. However, depending on the firewall’s load, it may take longer than one hour for these fields to update.
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