Access Control

The following topics explain access control rules. These rules control which traffic is allowed to pass through the device, and apply advanced services to the traffic, such as intrusion inspection.

Access Control Overview

The following topics explain access control policies.

Access Control Rules and the Default Action

Use the access control policy to allow or block access to network resources. The policy consists of a set of ordered rules, which are evaluated from top to bottom. The rule applied to traffic is the first one where all the traffic criteria are matched.

You can control access based on:

  • Traditional network characteristics such as source and destination IP addresses, protocol, ports, and interfaces (in the form of security zones).

  • The application that is being used. You can control access based on the specific application, or you can create rules that cover categories of applications, applications tagged with a particular characteristic, the type of application (client, server, web), or the application's risk or business relevance rating.

  • The destination URL of a web request, including the generalized category of the URL. You can refine category matches based on the public reputation of the target site.

  • The user who is making the request, or the user groups to which the user belongs.

For unencrypted traffic that you allow, you can apply IPS inspection to check for threats and block traffic that appears to be an attack. You can also use file policies to check for prohibited files or malware.

Any traffic that does not match an access rule is handled by the access control Default Action. If you allow traffic by default, you can apply intrusion inspection to the traffic. However, you cannot perform file or malware inspection on traffic handled by the default action.

Application Filtering

You can use access control rules to filter traffic based on the application used in the connection. The system can recognize a wide variety of applications, so that you do not need to figure out how to block one web application without blocking all web applications.

For some popular applications, you can filter on different aspects of the application. For example, you could create a rule that blocks Facebook Games without blocking all of Facebook.

You can also create rules based on general application characteristics, blocking or allowing entire groups of applications by selecting risk or business relevance, type, category, or tag. However, as you select categories in an application filter, look over the list of matching applications to ensure you are not including unintended applications. For a detailed explanation of the possible groupings, see Application Criteria.

Application Control for Encrypted and Decrypted Traffic

If an application uses encryption, the system might not be able to identify the application.

The system can detect application traffic encrypted with StartTLS, including SMTPS, POPS, FTPS, TelnetS, and IMAPS. In addition, it can identify certain encrypted applications based on the Server Name Indication in the TLS ClientHello message, or the subject distinguished name value from the server certificate.

Use the application filters dialog box to determine if your application requires decryption by selecting the following Tags, then examining the list of applications.

  • SSL Protocol—You do not need to decrypt traffic tagged as SSL Protocol. The system can recognize this traffic and apply your access control action. Access control rules for the listed applications should match to expected connections.

  • Decrypted Traffic—The system can recognize this traffic only if you first decrypt the traffic. Because you cannot configure SSL decryption using FDM, access control rules for these applications do not work. For example, at the time of this writing, Dropbox has this tag. Thus, access rules for the Dropbox application will not match Dropbox connections.

Best Practices for Application Filtering

Please keep the following recommendations in mind when designing your application filtering access control rules.

  • To handle traffic referred by a web server, such as advertisement traffic, match the referred application rather than the referring application.

  • Avoid combining application and URL criteria in the same rule, especially for encrypted traffic.

  • If you write a rule for traffic that is tagged Decrypted Traffic, ensure that you have an SSL Decryption rule that will decrypt the matching traffic. These applications can be identified in decrypted connections only.

  • The system can detect multiple types of Skype application traffic. To control Skype traffic, choose the Skype tag from the Application Filters list rather than selecting individual applications. This ensures that the system can detect and control all Skype traffic the same way.

  • To control access to Zoho mail, select both the Zoho and Zoho Mail applications.

URL Filtering

You can use access control rules to filter traffic based on the URL used in an HTTP or HTTPS connection. Note that URL filtering for HTTP is more straight-forward than it is for HTTPS, because HTTPS is encrypted.

You can use the following techniques to implement URL filtering.

  • Category and reputation-based URL filtering—With a URL filtering license, you can control access to web sites based on the URL’s general classification (category) and risk level (reputation). This is by far the easiest and most effective way to block unwanted sites.

  • Manual URL filtering—With any license, you can manually specify individual URLs, and groups of URLs, to achieve granular, custom control over web traffic. The main purpose of manual filtering is to create exceptions to category-based block rules, but you can use manual rules for other purposes.

The following topics provide more information on URL filtering.

Filtering URLs by Category and Reputation

With a URL filtering license, you can control access to web sites based on the category and reputation of the requested URLs:

  • Category—A general classification for the URL. For example, ebay.com belongs to the Auctions category, and monster.com belongs to the Job Search category. A URL can belong to more than one category.

  • Reputation—How likely the URL is to be used for purposes that might be against your organization’s security policy. Reputations range from High Risk (level 1) to Well Known (level 5).

URL categories and reputations help you quickly configure URL filtering. For example, you can use access control to block high risk URLs in the Abused Drugs category.

Using category and reputation data also simplifies policy creation and administration. Sites that represent security threats, or that serve undesirable content, might appear and disappear faster than you can update and deploy new policies. As Cisco updates the URL database with new sites, changed classifications, and changed reputations, your rules automatically adjust to the new information. You do not need to edit your rules to account for new sites.

If you enable regular URL database updates, you can ensure that the system uses up-to-date information for URL filtering. You can also enable communications with Cisco Collective Security Intelligence (CSI) to obtain the latest threat intelligence for URLs with unknown category and reputation. For more information, see Configuring URL Filtering Preferences.


Note

To see URL category and reputation information in events and application details, you must create at least one rule with a URL condition.

Looking Up the Category and Reputation for a URL

You can check on the category and reputation for a particular URL by using the following site. You can use this information to help you check the behavior of your category and reputation based URL filtering rules.

https://www.brightcloud.com/tools/url-ip-lookup.php

Manual URL Filtering

You can supplement or selectively override category and reputation-based URL filtering by manually filtering individual URLs or groups of URLs. You can perform this type of URL filtering without a special license.

For example, you might use access control to block a category of web sites that are not appropriate for your organization. However, if the category contains a web site that is appropriate, and to which you want to provide access, you can create a manual Allow rule for that site and place it before the Block rule for the category.

To configure manual URL filtering, you create a URL object with the destination URL. How this URL is interpreted is based on the following rules:

  • If you do not include a path (that is, there is no / character in the URL), the match is based on the server’s hostname only. The hostname is considered a match if it comes after the :// separator, or after any dot in the hostname. For example, ign.com matches ign.com and www.ign.com, but it does not match verisign.com.

  • If you include one or more / character, the entire URL string is used for a substring match, including the server name, path, and any query parameters. However, we recommend that you do not use manual URL filtering to block or allow individual web pages or parts of sites, as servers can be reorganized and pages moved to new paths. Substring matching can also lead to unexpected matches, where the string you include in the URL object also matches paths on unintended servers or strings within query parameters.

  • The system disregards the encryption protocol (HTTP vs HTTPS). In other words, if you block a website, both HTTP and HTTPS traffic to that website is blocked, unless you use an application condition to target a specific protocol. When creating a URL object, you do not need to specify the protocol when creating an object. For example, use example.com rather than http://example.com.

  • If you plan to use a URL object to match HTTPS traffic in an access control rule, create the object using the subject common name in the public key certificate used to encrypt the traffic. Also, the system disregards subdomains within the subject common name, so do not include subdomain information. For example, use example.com rather than www.example.com.

    However, please understand that the subject common name in the certificate might be completely unrelated to a web site’s domain name. For example, the subject common name in the certificate for youtube.com is *.google.com (this of course might change at any time). You will get more consistent results if you use the SSL Decryption policy to decrypt HTTPS traffic so that URL filtering rules work on decrypted traffic.


    Note

    URL objects will not match HTTPS traffic if the browser resumes a TLS session because the certificate information is no longer available. Thus, even if you carefully configure the URL object, you might get inconsistent results for HTTPS connections.

Filtering HTTPS Traffic

Because HTTPS traffic is encrypted, performing URL filtering directly on HTTPS traffic is not as straight-forward as it is on HTTP traffic. For that reason, you should consider using SSL Decryption policies to decrypt all HTTPS traffic that you intend to filter. That way, the URL filtering access control policies work on decrypted traffic, and you get the same results you would get for regular HTTP traffic.

However, if you do intend to allow some HTTPS traffic to pass undecrypted into the access control policy, you need to understand that rules match HTTPS traffic differently than they do for HTTP traffic. To filter encrypted traffic, the system determines the requested URL based on information passed during the SSL handshake: the subject common name in the public key certificate used to encrypt the traffic. There might be little or no relationship between the web site hostname in the URL and the subject common name.

HTTPS filtering, unlike HTTP filtering, disregards subdomains within the subject common name. Do not include subdomain information when manually filtering HTTPS URLs. For example, use example.com rather than www.example.com. Also, review the content of the certificates used by the site to ensure you have the right domain, the one used in the subject common name, and that this name will not conflict with your other rules (for example, the name for a site you want to block might overlap with one you want to allow). For example, the subject common name in the certificate for youtube.com is *.google.com (this of course might change at any time).


Note

URL objects will not match HTTPS traffic if the browser resumes a TLS session because the certificate information is no longer available. Thus, even if you carefully configure the URL object, you might get inconsistent results for HTTPS connections.

Controlling Traffic by Encryption Protocol

The system disregards the encryption protocol (HTTP vs HTTPS) when performing URL filtering. This occurs for both manual and reputation-based URL conditions. In other words, URL filtering treats traffic to the following web sites identically:

  • http://example.com

  • https://example.com

To configure a rule that matches only HTTP or HTTPS traffic, but not both, either specify the TCP port in the Destination condition or add an application condition to the rule. For example, you could allow HTTPS access to a site while disallowing HTTP access by constructing two access control rules, each with an TCP port or application, and URL, condition.

The first rule allows HTTPS traffic to the website:

  • Action: Allow
  • TCP port or Application: HTTPS (TCP port 443)
  • URL: example.com

The second rule blocks HTTP access to the same website:

  • Action: Block
  • TCP port or Application: HTTP (TCP port 80)
  • URL: example.com

Comparing URL and Application Filtering

URL and application filtering have similarities. But you should use them for very distinct purposes:

  • URL filtering is best used to block or allow access to an entire web server. For example, if you do not want to allow any type of gambling on your network, you can create a URL filtering rule to block the Gambling category. With this rule, users cannot get to any pages on any web server within the category.

  • Application filtering is useful for blocking specific applications regardless of the hosting site, or for blocking specific features of an otherwise allowable web site. For example, you could block just the Facebook Games application without blocking all of Facebook.

Because combining application and URL criteria can lead to unexpected results, especially for encrypted traffic, it is a good policy to create separate rules for URL and application criteria. If you do need to combine application and URL criteria in a single rule, you should place these rules after straight-forward application-only or URL-only rules, unless the application+URL rule is acting as an exception to a more general application-only or URL-only rule. Because URL filtering block rules are more broad than application filtering, you should place them above application-only rules.

If you do combine application and URL criteria, you might need to monitor your network more carefully to ensure that you are not allowing access to unwanted sites and applications.

Best Practices for Effective URL Filtering

Please keep the following recommendations in mind when designing your URL filtering access control rules.

  • Use category and reputation blocking whenever possible. This ensures that new sites get blocked automatically as they are added to the categories, and that blocking based on reputation is adjusted if a site becomes more (or less) reputable.

  • When using URL category matching, note that there are cases where the login page for a site is in a different category than the site itself. For example, Gmail is in the Web-based Email category, whereas the login page is in the Internet Portals category. If you have different rules with different actions for the categories, you might get unintended results.

  • Use URL objects to target entire web sites and to make exceptions to category blocking rules. That is, to allow specific sites that would otherwise get blocked in a category rule.

  • For the most effective filtering of HTTPS connections, implement SSL decryption rules to decrypt traffic for which you are writing an access control rule. Any decrypted HTTPS connections are filtered as HTTP connections in the access control policy, so you avoid all of the limitations for HTTPS filtering.

  • Place URL blocking rules before any application filtering rules, because URL filtering blocks entire web servers, whereas application filtering targets specific application usage regardless of the web server.

What the User Sees When You Block Web Sites

When you block web sites with URL filtering rules, what the user sees differs based on whether the site is encrypted.

  • HTTP connections—The user sees a system default block response page instead of the normal browser page for timed out or reset connections. This page should make it clear that you blocked the connection on purpose.

  • HTTPS (encrypted) connections—The user does not see the system default block response page. Instead, the user sees the browser’s default page for a secure connection failure. The error message does not indicate the site was blocked due to policy. Instead, errors might indicate that there are no common encryption algorithms. It will not be obvious from this message that you blocked the connection on purpose.

In addition, web sites might be blocked by other access control rules that are not explicitly URL filtering rules, or even by the default action. For example, if you block entire networks or geolocations, any web sites on that network or in that geographic location are also blocked. Users blocked by these rules may, or may not, get a response page as described in the limitations below.

If you implement URL filtering, consider explaining to end users what they might see when a site is intentionally blocked, and what types of site you are blocking. Otherwise, they might spend a good deal of time troubleshooting blocked connections.

Limitations of HTTP Response Pages

HTTP response pages do not always appear when the system blocks web traffic.

  • The system does not display a response page when web traffic is blocked as a result of a promoted access control rule (an early-placed blocking rule with only simple network conditions).

  • The system does not display a response page when web traffic is blocked before the system identifies the requested URL.

  • The system does not display a response page for encrypted connections blocked by access control rules.

Intrusion, File, and Malware Inspection

Intrusion and file policies work together as the last line of defense before traffic is allowed to its destination:

  • Intrusion policies govern the system's intrusion prevention capabilities.

  • File policies govern the system's file control and malware defense capabilities.

All other traffic handling occurs before network traffic is examined for intrusions, prohibited files, and malware. By associating an intrusion or file policy with an access control rule, you are telling the system that before it passes traffic that matches the access control rule's conditions, you first want to inspect the traffic with an intrusion policy, a file policy, or both.

You can configure intrusion and file policies on rules that allow traffic only. Inspection is not performed on rules set to trust or block traffic. In addition, if the default action for the access control policy is allow, you can configure an intrusion policy but not a file policy.

For any single connection handled by an access control rule, file inspection occurs before intrusion inspection. That is, the system does not inspect files blocked by a file policy for intrusions. Within file inspection, simple blocking by type takes precedence over malware inspection and blocking. Until a file is detected and blocked in a session, packets from the session may be subject to intrusion inspection.


Note

By default, the system disables intrusion and file inspection of encrypted payloads. This helps reduce false positives and improve performance when an encrypted connection matches an access control rule that has intrusion and file inspection configured. Inspection works with unencrypted traffic only.

Best Practices for Access Control Rule Order

Rules are applied on a first-match basis, so you must ensure that rules with highly specific traffic matching criteria appear above policies that have more general criteria that would otherwise apply to the matching traffic. Consider the following recommendations:

  • Specific rules should come before general rules, especially when the specific rules are exceptions to general rules.

  • Any rules that drop traffic based on layer-3/4 criteria only (such as IP address, security zone, and port number) should come as early as possible. We recommend they come before any rule that requires inspection, such as those with application or URL criteria, because Layer-3/4 criteria can be evaluated quickly and without inspection. Of course, any exceptions to these rules must be placed above them.

  • Whenever possible, put specific drop rules near the top of the policy. This ensures the earliest possible decision on undesirable traffic.

  • Any rules that include both application and URL criteria should come after straight-forward application-only or URL-only rules, unless the application+URL rule is acting as an exception to a more general application-only or URL-only rule. Combining application and URL criteria can lead to unexpected results, especially for encrypted traffic, so we recommend that you create separate rules for URL and application filtering whenever possible.

NAT and Access Rules

Access rules always use the real IP addresses when determining an access rule match, even if you configure NAT. For example, if you configure NAT for an inside server, 10.1.1.5, so that it has a publicly routable IP address on the outside, 209.165.201.5, then the access rule to allow the outside traffic to access the inside server needs to reference the server’s real IP address (10.1.1.5), and not the mapped address (209.165.201.5).

How Other Security Policies Impact Access Control

Other security policies can affect how access control rules function and match connections. As you configure your access rules, keep the following in mind:

  • Identity policy—Connections are matched to users (and thus, user groups) only if there is a user mapping for the source IP address. Access rules that key on user or group membership can match only those connections for which user identity was successfully collected by your identity policy.

  • VPN (site-to-site or remote access)—VPN traffic is always evaluated against the access control policy, and connections are allowed or dropped based on the matching rule. However, the VPN tunnel itself is decrypted before the access control policy is evaluated. The access control policy evaluates the connections that are embedded within the VPN tunnel, not the tunnel itself.

License Requirements for Access Control

You do not need a special license to use the access control policy.

However, you do need the following licenses for specific features within the access control policy. For information on configuring licenses, see Enabling or Disabling Optional Licenses.

  • URL license—To create rules that use URL categories and reputations as match criteria.

  • Threat license—To configure an intrusion policy on an access rule or the default action. You also need this license to use a file policy (the Malware license is also required).

  • Malware license—To configure a file policy on an access rule. The Threat is also required for file policies.

Guidelines and Limitations for Access Control Policies

Following are some additional limitations for access control. Please consider them when evaluating whether you are getting the expected results from your rules.

  • FDM can download information on up to 2000 users from the directory server. If your directory server includes more than 2000 user accounts, you will not see all possible names when selecting users in an access rule or when viewing user-based dashboard information. You can write rules on only those names that were downloaded.

    The 2000 limit also applies to the names associated with groups. If a group has more than 2000 members, only the 2000 names that were downloaded can be matched against the group membership.

  • If a Vulnerability Database (VDB) update removes (deprecates) applications, you must make changes to any access control rules or application filters that use the application that was deleted. You cannot deploy changes until you fix these rules. In addition, you cannot install system software updates before fixing the issue. On the Application Filters object page, or the Application tab of the rule, these applications say “(Deprecated)” after the application name.

  • If you edit a rule that is actively in use, the changes do not apply to established connections that are no longer being inspected by Snort. The new rule is used to match against future connections. In addition, if Snort is actively inspecting a connection, it can apply the changed matching or action criteria to an existing connection. If you need to ensure that your changes apply to all current connections, you can log into the device CLI and use the clear conn command to end established connections, on the assumption that the sources for the connections will then attempt to reestablish the connection and thus be matched appropriately against the new rule.

  • It takes 3 to 5 packets for the system to identify the application or URL in a connection. Thus, the correct access control rule might not be matched immediately for a given connection. However, once the application/URL is known, the connection is handled based on the matching rule. For encrypted connections, this happens after the server certificate exchange in the SSL handshake.

  • The system applies the default policy action to packets that do not have a payload in a connection where an application is identified.

  • Leave matching criteria empty whenever possible, especially those for security zones, network objects, and port objects. For example, the system can more efficiently match traffic for all interfaces if you simply leave the security zone criteria blank, rather than if you create zones that contain all interfaces. When you specify multiple criteria, the system must match against every combination of the contents of the criteria you specify.

  • If you specify IP addresses for source or destination criteria, do not mix IPv4 and IPv6 addresses in the same rule. Create separate rules for IPv4 and IPv6 addresses.

  • Due to memory limitations, some device models perform most URL filtering with a smaller, less granular, set of categories and reputations. For example, even if a parent URL's subsites have different URL categories and reputations, some devices may only store the parent URL's data. For web traffic handled by these devices, the system may perform cloud lookups to determine category and reputation for sites not in the local database. Lower-memory devices include the following ASA models: 5506-X, 5506H-X, 5506W-X, 5508-X, 5512-X, 5515-X, 5516-X, and 5525-X.

  • GRE tunnels that violate the related RFCs will be dropped. For example, if a GRE tunnel contains non-zero values in the reserved bits, contrary to the RFCs, it is dropped. If you need to allow non-compliant GRE tunnels, you need to use a remote manager and configure a prefilter rule that trusts the sessions. You cannot configure prefilter rules using the FDM.

Configuring the Access Control Policy

Use the access control policy to control access to network resources. The policy consists of a set of ordered rules, which are evaluated from top to bottom. The rule applied to traffic is the first one where all the traffic criteria are matched. If no rules match the traffic, the default action shown at the bottom of the page is applied.

To configure the access control policy, select Policies > Access Control.

The access control table lists all rules in order. For each rule:

  • Click the > button next to the rule number in the left-most column to open the rule diagram. The diagram can help you visualize how the rule controls traffic. Click the button again to close the diagram.

  • Most cells allow inline editing. For example, you can click the action to select a different one, or click a source network object to add or change the source criteria.

  • To move a rule, hover over the rule until you get the move icon (Move rule icon.), then click, drag, and drop the rule to the new location. You can also move a rule by editing it and selecting the new location in the Order list. It is critical that you put the rules in the order that you want them processed. Specific rules should be near the top, especially for rules that define exceptions to more general rules

  • The right-most column contains the action buttons for a rule; mouse over the cell to see the buttons. You can edit (edit icon) or delete (delete icon) a rule.

The following topics explain how to configure the policy.

Configuring the Default Action

If a connection does not match a specific access rule, it is handled by the default action for the access control policy.

Procedure

Step 1

Select Policies > Access Control.

Step 2

Click anywhere in the Default Action field.

Step 3

Select the action to apply to matching traffic.

  • Trust—Allow traffic without further inspection of any kind.
  • Allow—Allow the traffic subject to the intrusion policy.
  • Block—Drop the traffic unconditionally. The traffic is not inspected.
Step 4

If the action is Allow, select Enable Policy > On under Intrusion Policy and select an intrusion policy.

For an explanation of the policy options, see Intrusion Policy Settings.

Step 5

(Optional.) Configure logging for the default action.

You must enable logging for traffic that matches the default action to be included in dashboard data or Event Viewer. See Logging Settings.

Step 6

Click OK.

Configuring Access Control Rules

Use access control rules to control access to network resources. Rules in the access control policy are evaluated from top to bottom. The rule applied to traffic is the first one where all the traffic criteria are matched.

Procedure

Step 1

Select Policies > Access Control.

Step 2

Do any of the following:

  • To create a new rule, click the + button.
  • To edit an existing rule, click the edit icon (edit icon) for the rule.

To delete a rule you no longer need, click the delete icon (delete icon) for the rule.

Step 3

In Order, select where you want to insert the rule in the ordered list of rules.

Rules are applied on a first-match basis, so you must ensure that rules with highly specific traffic matching criteria appear above policies that have more general criteria that would otherwise apply to the matching traffic.

The default is to add the rule to the end of the list. If you want to change a rule's location later, edit this option.

Step 4

In Title, enter a name for the rule.

The name cannot contain spaces. You can use alphanumeric characters and these special characters: + . _ -

Step 5

Select the action to apply to matching traffic.

  • Trust—Allow traffic without further inspection of any kind.
  • Allow—Allow the traffic subject to the intrusion and other inspection settings in the policy.
  • Block—Drop the traffic unconditionally. The traffic is not inspected.
Step 6

Define the traffic matching criteria using any combination of the following tabs:

  • Source/Destination—The security zones (interfaces) through which the traffic passes, the IP addresses or the country or continent (geographical location) for the IP address, or the protocols and ports used in the traffic. The default is any zone, address, geographical location, protocol, and port. See Source/Destination Criteria.
  • Application—The application, or a filter that defines applications by type, category, tag, risk, or business relevance. The default is any application. See Application Criteria.
  • URL—The URL or URL category of a web request. The default is any URL. See URL Criteria.
  • Users—The user or user group. Your identity policies determine whether user and group information is available for traffic matching. You must configure identity policies to use this criteria. See User Criteria.

To modify a condition, you click the + button within that condition, select the desired object or element, and click OK in the popup dialog box. If the criterion requires an object, you can click Create New Object if the object you require does not exist. Click the x for an object or element to remove it from the policy.

When adding conditions to access control rules, consider the following tips:

  • You can configure multiple conditions per rule. Traffic must match all the conditions in the rule for the rule to apply to traffic. For example, you can use a single rule to perform URL filtering for specific hosts or networks.

  • For each condition in a rule, you can add up to 50 criteria. Traffic that matches any of a condition's criteria satisfies the condition. For example, you can use a single rule to apply application control for up to 50 applications or application filters. Thus, there is an OR relationship among the items in a single condition, but an AND relationship between condition types (for example, between source/destination and application).

  • Some features require that you enable the appropriate license.

Step 7

(Optional.) For policies that use the Allow action, you can configure further inspection on unencrypted traffic. Click one of the following links:

  • Intrusion Policy—Select Intrusion Policy > On and select the intrusion inspection policy to inspect traffic for intrusions and exploits. See Intrusion Policy Settings.
  • File Policy—Select the file policy to inspect traffic for files that contain malware and for files that should be blocked. See File Policy Settings.
Step 8

(Optional.) Configure logging for the rule.

By default, connection events are not generated for traffic that matches a rule, although file events are generated by default if you select a file policy. You can change this behavior. You must enable logging for traffic that matches the policy to be included in dashboard data or Event Viewer. See Logging Settings.

Intrusion events are always generated for intrusion rules set to drop or alert regardless of the logging configuration on the matching access rule.

Step 9

Click OK.

Source/Destination Criteria

The Source/Destination criteria of an access rule define the security zones (interfaces) through which the traffic passes, the IP addresses or the country or continent (geographical location) for the IP address, or the protocols and ports used in the traffic. The default is any zone, address, geographical location, protocol, and port.

To modify a condition, you click the + button within that condition, select the desired object or element, and click OK. If the criterion requires an object, you can click Create New Object if the object you require does not exist. Click the x for an object or element to remove it from the policy.

You can use the following criteria to identify the source and destination to match in the rule.

Source Zones, Destination Zones

The security zone objects that define the interfaces through which the traffic passes. You can define one, both, or neither criteria: any criteria not specified applies to traffic on any interface.

  • To match traffic leaving the device from an interface in the zone, add that zone to the Destination Zones.

  • To match traffic entering the device from an interface in the zone, add that zone to the Source Zones.

  • If you add both source and destination zone conditions to a rule, matching traffic must originate from one of the specified source zones and egress through one of the destination zones.

Use this criteria when the rule should apply based on where the traffic enters or exits the device. For example, if you want to ensure that all traffic going to inside hosts gets intrusion inspection, you would select your inside zone as the Destination Zones while leaving the source zone empty. To implement intrusion filtering in the rule, the rule action must be Allow, and you must select an intrusion policy in the rule.

Source Networks, Destination Networks

The network objects or geographical locations that define the network addresses or locations of the traffic.

  • To match traffic from an IP address or geographical location, configure the Source Networks.

  • To match traffic to an IP address or geographical location, configure the Destination Networks.

  • If you add both source and destination network conditions to a rule, matching traffic must originate from one of the specified IP addresses and be destined for one of the destination IP addresses.

When you add this criteria, you select from the following tabs:

  • Network—Select the network objects or groups that define the source or destination IP addresses for the traffic you want to control.

  • Geolocation—Select the geographical location to control traffic based on its source or destination country or continent. Selecting a continent selects all countries within the continent. Besides selecting geographical location directly in the rule, you can also select a geolocation object that you created to define the location. Using geographical location, you could easily restrict access to a particular country without needing to know all of the potential IP addresses used there.


    Note

    To ensure that you are using up-to-date geographical location data to filter your traffic, Cisco strongly recommends that you regularly update the geolocation database (GeoDB).

Source Ports, Destination Ports/Protocols

The port objects that define the protocols used in the traffic. For TCP/UDP, this can include ports. For ICMP, it can include codes and types.

  • To match traffic from a protocol or port, configure the Source Ports. Source ports can be TCP/UDP only.

  • To match traffic to a protocol or port, configure the Destination Ports/Protocols. If you add only destination ports to a condition, you can add ports that use different transport protocols. ICMP and other non-TCP/UDP specifications are allowed in destination ports only; they are not allowed in source ports.

  • To match traffic both originating from specific TCP/UDP ports and destined for specific TCP/UDP ports, configure both. If you add both source and destination ports to a condition, you can only add ports that share a single transport protocol, TCP or UDP. For example, you could target traffic from port TCP/80 to port TCP/8080.

Application Criteria

The Application criteria of an access rule defines the application used in an IP connection, or a filter that defines applications by type, category, tag, risk, or business relevance. The default is any application.

Although you can specify individual applications in the rule, application filters simplify policy creation and administration. For example, you could create an access control rule that identifies and blocks all high risk, low business relevance applications. If a user attempts to use one of those applications, the session is blocked.

In addition, Cisco frequently updates and adds additional application detectors via system and vulnerability database (VDB) updates. Thus, a rule blocking high risk applications can automatically apply to new applications without you having to update the rule manually.

You can specify applications and filters directly in the rule, or create application filter objects that define those characteristics. The specifications are equivalent, although using objects can make it easier to stay within the 50-items-per-criteria system limit if you are creating a complex rule.

To modify the application and filters list, you click the + button within the condition, select the desired applications or application filter objects, which are listed on separate tabs, and click OK in the popup dialog box. On either tab, you can click Advanced Filter to select filter criteria or to help you search for specific applications. Click the x for an application, filter, or object to remove it from the policy. Click the Save As Filter link to save the combined criteria that is not already an object as a new application filter object.


Note

If a selected application was removed by a VDB update, “(Deprecated)” appears after the application name. You must remove these applications from the filter, or subsequent deployments and system software upgrades will be blocked.

You can use the following Advanced Filter criteria to identify the application or filter to match in the rule. These are the same elements used in application filter objects.


Note

Multiple selections within a single filter criteria have an OR relationship. For example, Risk is High OR Very High. The relationship between filters is AND, so Risk is High OR Very High, AND Business Relevance is Low OR Very Low. As you select filters, the list of applications in the display updates to show only those that meet the criteria. You can use these filters to help you find applications that you want to add individually, or to verify that you are selecting the desired filters to add to the rule.

Risks

The likelihood that the application is used for purposes that might be against your organization's security policy, from very low to very high.

Business Relevance

The likelihood that the application is used within the context of your organization's business operations, as opposed to recreationally, from very low to very high.

Types

The type of application:

  • Application Protocol—Application protocols such as HTTP and SSH, which represent communications between hosts.

  • Client Protocol—Clients such as web browsers and email clients, which represent software running on the host.

  • Web Application—Web applications such as MPEG video and Facebook, which represent the content or requested URL for HTTP traffic.

Categories

A general classification for the application that describes its most essential function.

Tags

Additional information about the application, similar to category.

For encrypted traffic, the system can identify and filter traffic using only the applications tagged SSL Protocol. Applications without this tag can only be detected in unencrypted or decrypted traffic. Also, the system assigns the decrypted traffic tag to applications that the system can detect in decrypted traffic only, not encrypted or unencrypted.

Applications List (bottom of the display)

This list updates as you select filters from the options above the list, so you can see the applications that currently match the filter. Use this list to verify that your filter is targeting the desired applications when you intend to add filter criteria to the rule. If your intention is to add specific applications, select them from this list.

URL Criteria

The URL criteria of an access rule defines the URL used in a web request, or the category to which the requested URL belongs. For category matches, you can also specify the relative reputation of sites to allow or block. The default is to allow all URLs.

URL categories and reputations allow you to quickly create URL conditions for access control rules. For example, you could block all Gambling sites, or high risk Social Networking sites. If a user attempts to browse to any URL with that category and reputation combination, the session is blocked.

Using category and reputation data also simplifies policy creation and administration. It grants you assurance that the system will control web traffic as expected. Finally, because Cisco's threat intelligence is continually updated with new URLs, as well as new categories and risks for existing URLs, you can ensure that the system uses up-to-date information to filter requested URLs. Malicious sites that represent security threats such as malware, spam, botnets, and phishing may appear and disappear faster than you can update and deploy new policies.

To modify the URL list, you click the + button within the condition and select the desired categories or URLs using one of the following techniques. Click the x for a category or object to remove it from the policy.

URL Tab

Click +, select URL objects or groups, and click OK. You can click Create New URL if the object you require does not exist.


Note

Before configuring URL objects to target specific sites, carefully read the information on manual URL filtering.

Categories Tab

Click +, select the desired categories, and click OK.

The default is to apply the rule to all URLs in each selected category regardless of reputation. To limit the rule based on reputation, click the down arrow for each category, deselect the Any checkbox, and then use the Reputation slider to choose the reputation level. The left of the reputation slider indicates sites that will be allowed, the right side are sites that will be blocked. How reputation is used depends on the rule action:

  • If the rule blocks or monitors web access, selecting a reputation level also selects all reputations more severe than that level. For example, if you configure a rule to block or monitor Suspicious sites (level 2), it also automatically blocks or monitors High risk (level 1) sites.

  • If the rule allows web access, selecting a reputation level also selects all reputations less severe than that level. For example, if you configure a rule to allow Benign sites (level 4), it also automatically allows Well known (level 5) sites.

User Criteria

The User criteria of an access rule defines the user or user group for an IP connection. You must configure identity policies and the associated directory server to include user or user group criteria in an access rule.

Your identity policies determine whether user identity is collected for a particular connection. If identity is established, the IP address of the host is associated with the identified user. Thus, traffic whose source IP address is mapped to a user is considered to be from that user. IP packets themselves do not include user identity information, so this IP-address-to-user mapping is the best approximation available.

Because you can add a maximum of 50 users or groups to a rule, selecting groups usually makes more sense than selecting individual users. For example, you could create a rule allowing the Engineering group access to a development network, and create a subsequent rule that denies all other access to the network. Then, to make the rule apply to new engineers, you only need to add the engineer to the Engineering group in the directory server.

To modify the users list, you click the + button within the condition and select the desired identities using one of the following techniques. Click the x for an identity to remove it from the policy.

  • Users and Groups tab—Select the desired users or user groups. Groups are available only if you configure groups in the directory server. If you select a group, the rule applies to any member of the group, including subgroups. If you want to treat a sub-group differently, you need to create a separate access rule for the sub-group and place it above the rule for the parent group in the access control policy.

  • Special Entities tab—Select from the following:

    • Failed Authentication—The user was prompted to authenticate, but failed to enter a valid username/password pair within the maximum number of allowed attempts. Failure to authenticate does not itself prevent the user from accessing the network, but you can write an access rule to limit network access for these users.

    • Guest—Guest users are like Failed Authentication users, except that your identity rule is configured to call these users Guest. Guest users were prompted to authenticate and failed to do so within the maximum number of attempts.

    • No Authentication Required—The user was not prompted to authentication, because the user's connections matched identity rules that specified no authentication.

    • Unknown—There is no user mapping for the IP address, and there is no record of failed authentication yet. Typically, this means that no HTTP traffic has yet been seen from that address.

Intrusion Policy Settings

Cisco delivers several intrusion policies with the Firepower System. These policies are designed by the Cisco Talos Intelligence Group (Talos), who set the intrusion and preprocessor rule states and advanced settings. You cannot modify these policies.

For access control rules that allow traffic, you can select one of the following intrusion policies to inspect traffic for intrusions and exploits. An intrusion policy examines decoded packets for attacks based on patterns, and can block or alter malicious traffic.

To enable intrusion inspection, select Intrusion Policy > On and select the desired policy. The policies are listed from least to most secure.

  • Connectivity over Security—This policy is built for organizations where connectivity (being able to get to all resources) takes precedence over network infrastructure security. The intrusion policy enables far fewer rules than those enabled in the Security over Connectivity policy. Only the most critical rules that block traffic are enabled. Select this policy if you want to apply some intrusion protection but you are fairly confident in the security of your network.

  • Balanced Security and Connectivity—This policy is designed to balance overall network performance with network infrastructure security. This policy is appropriate for most networks. Select this policy for most situations where you want to apply intrusion prevention.

  • Security over Connectivity—This policy is built for organizations where network infrastructure security takes precedence over user convenience. The intrusion policy enables numerous network anomaly intrusion rules that could alert on or drop legitimate traffic. Select this policy when security is paramount or for traffic that is high risk.

  • Maximum Detection—This policy is built for organizations where network infrastructure security is given even more emphasis than is given by the Security Over Connectivity policy, with the potential for even greater operational impact. For example, the intrusion policy enables rules in a large number of threat categories including malware, exploit kit, old and common vulnerabilities, and known in-the-wild exploits. If you select this policy, carefully evaluate whether too much legitimate traffic is being dropped.

File Policy Settings

Use file policies to detect malicious software, or malware, using malware defense. You can also use file policies to perform file control, which allows control over all files of a specific type regardless of whether the files contain malware.

Malware defense uses the AMP Cloud to retrieve dispositions for possible malware detected in network traffic, and to obtain local malware analysis and file pre-classification updates. The management interface must have a path to the Internet to reach the AMP Cloud and perform malware lookups. When the device detects an eligible file, it uses the file's SHA-256 hash value to query the AMP Cloud for the file's disposition. The possible dispositions are:

  • Malware—The AMP Cloud categorized the file as malware. An archive file (e.g. a zip file) is marked as malware if any file within it is malware.

  • Clean—The AMP Cloud categorized the file as clean, containing no malware. An archive file is marked as clean if all files within it are clean.

  • Unknown—The AMP Cloud has not assigned a disposition to the file yet. An archive file is marked as unknown if any file within it is unknown.

  • Unavailable—The system could not query the AMP Cloud to determine the file's disposition. You may see a small percentage of events with this disposition; this is expected behavior. If you see a number of "unavailable" events in succession, ensure that the Internet connection for the management address is functioning correctly.

Available File Policies

You can select one of the following file policies:

  • None—Do not evaluate transmitted files for malware and do no file-specific blocking. Select this option for rules where file transmissions are trusted or where they are unlikely (or impossible), or for rules where you are confident your application or URL filtering adequately protects your network.

  • Block Malware All—Query the AMP Cloud to determine if files traversing your network contain malware, then block files that represent threats.

  • Cloud Lookup All—Query the AMP Cloudto obtain and log the disposition of files traversing your network while still allowing their transmission.

  • Block Office Document and PDF Upload, Block Malware Others—Block users from uploading Microsoft Office documents and PDFs. Additionally, query the AMP Cloud to determine if files traversing your network contain malware, then block files that represent threats.

  • Block Office Documents Upload, Block Malware Others—Block users from uploading Microsoft Office documents. Additionally, query the AMP Cloud to determine if files traversing your network contain malware, then block files that represent threats.

Logging Settings

The logging settings for an access rule determine whether connection events are issued for traffic that matches the rule. You must enable logging to see events related to the rule in the Event Viewer. You must also enable logging for matching traffic to be reflected in the various dashboards you can use to monitor the system.

You should log connections according to the security and compliance needs of your organization. If your goal is to limit the number of events you generate and improve performance, only enable logging for the connections critical to your analysis. However, if you want a broad view of your network traffic for profiling purposes, you can enable logging for additional connections.


Caution

Logging blocked TCP connections during a Denial of Service (DoS) attack can affect system performance and overwhelm the database with multiple similar events. Before you enable logging for a Block rule, consider whether the rule is for an Internet-facing interface or other interface vulnerable to DoS attack.

You can configure the following logging actions.

Select Log Action

You can select one of the following actions:

  • Log at Beginning and End of Connection—Issue events at the start and end of a connection. Because end-of-connection events contain everything that start-of-connection events contain, plus all of the information that could be gleaned during the connection, Cisco recommends that you do not select this option for traffic that you are allowing. Logging both events can impact system performance. However, this is the only option allowed for blocked traffic.

  • Log at End of Connection—Select this option if you want to enable connection logging at the end of the connection, which is recommended for allowed or trusted traffic.

  • No Logging at Connection—Select this option to disable logging for the rule. This is the default.


Note

When an intrusion policy invoked by an access control rule detects an intrusion and generates an intrusion event, the system automatically logs the end of the connection where the intrusion occurred, regardless of the logging configuration of the rule. For connections where an intrusion was blocked, the action for the connection in the connection log is Block, with a reason of Intrusion Block, even though to perform intrusion inspection you must use an Allow rule.

File Events

Select Log Files if you want to enable logging of prohibited files or malware events. You must select a file policy in the rule to configure this option. The option is enabled by default if you select a file policy for the rule. Cisco recommends you leave this option enabled.

When the system detects a prohibited file, it automatically logs one of the following types of event:

  • File events, which represent detected or blocked files, including malware files.

  • Malware events, which represent detected or blocked malware files only.

  • Retrospective malware events, which are generated when the malware disposition for a previously detected file changes.

For connections where a file was blocked, the action for the connection in the connection log is Block even though to perform file and malware inspection you must use an Allow rule. The connection's Reason is either File Monitor (a file type or malware was detected), or Malware Block or File Block (a file was blocked).

Send Connection Events To

If you want to send a copy of the events to an external syslog server, select the server object that defines the syslog server. If the required object does not already exist, click Create New Syslog Server and create it. (To disable logging to a syslog server, select Any from the server list.)

Because event storage on the device is limited, sending events to an external syslog server can provide more long term storage and enhance your event analysis.

Monitoring Access Control Policies

The following topics explain how you can monitor the access control policy.

Monitoring Access Control Statistics in the Dashboards

Most of the data on the Monitoring dashboards are directly related to your access control policy. See Monitoring Traffic and System Dashboards.

  • Monitoring > Policies shows the most-hit access control rules and related statistics.

  • You can find general statistics on the Network Overview, Destinations, Ingress Zones, and Egress Zones dashboards.

  • You can find URL filtering results on the Web Categories and Destinations dashboards. You must have at least one URL filtering policy to see any information on the Web Categories dashboard.

  • You can find application filtering results on the Applications dashboard.

  • You can find user-based statistics on the Users dashboard. You must implement identity policies to collect user information.

  • You can find intrusion policy statistics on the Attackers and Targets dashboards. You must apply an intrusion policy to at least one access control rule to see any information on these dashboards.

  • You can find file policy and malware filtering statistics on the File Logs dashboard. You must apply a file policy to at least one access control rule to see any information on this dashboard.

  • Monitoring > Events also shows events for connections and data related to the access control rules.

Monitoring Access Control Policies in the CLI

You can also log into the device CLI and use the following commands to get more detailed information about access control policies and statistics.

  • show access-control-config displays summary information about the access control rules along with per-rule hit counts.

  • show access-list displays the access control lists (ACLs) that were generated from the access control rules. The ACLs provide an initial filter and attempt to provide quick decisions whenever possible, so that connections that should be dropped do not need to be inspected (and thus consume resources unnecessarily). This information includes hit counts.

  • show snort statistics displays information about the Snort inspection engine, which is the main inspector. Snort implements application filtering, URL filtering, intrusion protection, and file and malware filtering.

  • show conn displays information about the connections currently established through the interfaces.

  • show traffic displays statistics about traffic flowing through each interface.

  • show ipv6 traffic displays statistics about IPv6 traffic flowing through the device.

Examples for Access Control

The use case chapter includes several examples of implementing access control rules. Please see the following examples: