Custom Rules

Use custom rules to tailor how WAF identifies malicious traffic. This provides added flexibility for threat identification that allows you to target malicious traffic with minimal impact to legitimate traffic. Custom threat identification combined with rapid testing and deployment enables you to quickly address long-term and zero-day vulnerabilities.

The Custom rules capability requires WAF Premier or WAF Standard. If you currently have WAF Essentials or WAF Insights and would like to use custom rules, please contact your CDN account manager to upgrade to the full version.

Custom Rule Sets

A custom rule set defines how threats will be identified through rules. Each rule contains:

• Up to 6 conditions that define threat identification criteria.

• A rule ID and message that will be associated with threats identified by this rule.

  Assigning a unique ID and message to each rule makes it easy to identify threats detected as a result of a specific rule.

  A rule ID must be a number between 66,000,000 and 66,999,999.

A custom rule set may contain up to 10 rules.

Threat Identification

WAF identifies a threat when a request satisfies at least one rule in a custom rule set. A rule is satisfied when a match is found for one or more variable(s)A variable identifies the request element (e.g., request header, query string, or request body) that WAF will analyze. in each condition.

Example #1:

This example assumes that your custom rule set contains the following two rules:

Rule	Description
1	This rule contains a single condition with a single variable.
2	This rule contains the following conditions: The first condition contains a single variable. The second condition contains two variables.

Assuming the above configuration, WAF identifies a threat under either of the following circumstances:

• A match is found for the variable defined in the first rule's condition.

• A match is found for the variable defined in the second rule's first condition.

  AND

  A match is found for either of the variables defined in the second rule's second condition.

Certain variables match on key-value pairs. If you match on multiple keys within a single variable, WAF will only need to find one of those matches to satisfy that variable. For example, if you set up a request header variable to match for Authorization and Content-Type, then requests that contain either or both of those headers will satisfy that variable.

Conditions

A condition determines how requests will be identified through variables, operators, match values, transformations, and negative matching.

Variables

A variable identifies the request element that WAF will analyze. We support the following request elements:

• ASN: Identifies requests by the Autonomous System Number (ASN) associated with the client's IP address.

  Specify a regular expression to match for multiple ASNs.
  Example: 
  Use the following pattern to match for requests from either 15133 or 14153:
  15133|14153

• Country: Identifies requests by the country from which the request originated. Specify the desired country using a country code.

  Specify a regular expression to match for multiple country codes.
  Example: 
  Use the following pattern to match for requests from the United States, Canada, or Mexico:
  US|CA|MX

• IP address: Identify requests by the requester's IP address. Specify a comma-delimited list of the desired IP address(es) using standard IPv4/IPv6 and CIDR notation. Specify a subnet by appending a slash (/) and the desired bit-length of the prefix (e.g., 11.22.33.0/22). Do not specify more than 1,000 IP addresses or IP blocks.

  Identifying requests by IP address is only supported when a condition contains a single variable.

  Example:

  192.0.2.20,203.0.113.0/24,2001:DB8::/32

• Request body parsed: Match against all or specific key-value pair(s) in the request body for a URL-encoded or JSON POST request:

  • All: Do not specify a key within this variable and specify the desired value or pattern within the Match value option.

  • Specific Key-Value Pair: Define the name of the desired key within this variable and specify the desired value or pattern within the Match value option.

    Setting up a request body parsed variable also allows you to define whether WAF uses a regular expression, a negative match, or both when comparing the value assigned to the variable against key names. Use a negative match to find requests whose payload does not contain the specified key.

  Use the Request body raw variable to match against the URL-encoded request body for any type of request (e.g., XML).

  WAF only inspects the first 8 KB of the request body. You may restrict the request body for valid requests to 8 KB (8,192 bytes) through a managed rule.

  Example:

  Match against the following request body by setting the the Match value option to blue. Require that this value be assigned to the sky key by also setting the request body parsed variable to sky.

  {
  	"id": "srZf45oP34p",	
  	"sky": "blue"
  }

• Request body raw: Match against a URL-encoded request body for any type of request (e.g., XML).

  WAF only inspects the first 8 KB of the request body. You may restrict the request body for valid requests to 8 KB (8,192 bytes) through a managed rule.

• Request cookies: Match against all or specific cookies.

  • All: Do not specify the desired cookie within this variable and specify the desired cookie value or pattern within the Match value option.

  • Specific Cookies: Define the name of the desired cookie within this variable and specify the desired cookie value or pattern within the Match value option.

    Setting up a cookie variable also allows you to define whether WAF uses a regular expression, a negative match, or both when comparing the value assigned to the variable against cookies. Use a negative match to find requests whose payload does not contain the specified cookie.

• Request header: Match against all or specific request headers.

  • All: Do not specify the desired request header within this variable and specify the desired header value or pattern within the Match value option.

  • Specific Request Headers: Define the name of the desired request header within this variable and specify the desired header value or pattern within the Match value option.

    Setting up a request header variable also allows you to define whether WAF uses a regular expression, a negative match, or both when comparing the value assigned to the variable against request headers. Use a negative match to find requests whose payload does not contain the specified request header.

• Request method: Match against request method (e.g., GET and POST).

• Request query: Match against the request's query string. Specify the desired value or pattern within the Match value option.

• Request URI: Match against the request's URL path and query string. Define a URL path that starts directly after the hostname. Exclude the protocol and hostname when defining this property.

  WAF does not transform edge CNAME URLs to CDN URLs prior to performing this comparison.

  Sample values:

  /marketing?id=123456

  /resources/images

• Request URL path: Match against the request's URL path. Define a URL path that starts directly after the hostname. Exclude the protocol, hostname, and query string when defining this property.

  Our service does not transform edge CNAME URLs to CDN URLs prior to performing this comparison.

  Sample values:

  /marketing

  /resources/images

All variables support the ability to match on the number of times that a request element is found within the request. Set up a variable to match on the number of instances instead of inspecting the element for a specific value or regular expression pattern by marking the Count option.

You may define zero or more keys when setting up variables that match on key-value pairs. WAF must find at least one of the specified keys in the request before that variable will be satisfied. For example, if you set up a request header variable to match for Authorization and Content-Type, then requests that contain either or both of those headers will satisfy that variable.

Operators

An operator determines how WAF will compare a match value against the request element identified by a variable.

• Begins with: A match is found when the request element starts with the specified match value.
• Contains: A match is found when the request element contains the specified match value.
• Ends with:  A match is found when the request element ends with the specified match value.

• Exact match:  A match is found when the request element is an exact match to the specified match value.

  Avoid enabling the Negative match option with the Exact match operator. This configuration will not yield the expected set of matches.

• Regex: A match is found when the request element satisfies the regular expression defined in the match value.

• Value match: A match is found when the request element occurs the exact number of times defined in the match value.

  The Value match operator should only be used when the Count option has been enabled.

Match Value

WAF uses a match value to identify threats.

• Default: By default, WAF compares a match value against the request element identified by a variable (e.g., URL path or a request header's value).
• Count: Enable the Count option on a variable to compare this value against the number of times that the request element identified by a variable (e.g., a specific cookie or request header) occurs within the request.

Example:

This example assumes the following configuration:

We will now examine how the Count option affects comparisons for this configuration.

• Disabled: If the Count option has been disabled on the variable, then WAF will compare the value of the Authentication request header to 1.
• Enabled: If the Count option has been enabled on the variable, then WAF will compare the number of times that the Authentication request header occurred in the request to 1.

The type of comparison that will be performed is determined by the Operator option.

Custom Rule Administration

You may create, modify, and delete custom rule sets.

Key information:

• Administer custom rule sets from the Custom Rules page.
• Apply a custom rule set to production traffic by adding it to a Security Application Manager configuration and then determining how it will be enforced. Multiple Security Application Manager configurations may use the same custom rule set. Leverage this capability to tailor security screening by application or traffic profile.
• It may take up to 2 minutes for an updated custom rule set to be applied across our entire network.

To create a custom rule set

1. Navigate to the Custom Rules page. How?From the main menu, navigate to More | Security | WAF Tier | Security Rule Manager | Custom Rules.

2. Click Add Custom Rule Profile.
3. In the Name option, type the unique name by which this custom rule set will be identified. This name should be sufficiently descriptive to identify it when setting up a Security Application Manager configuration.
4. Each new custom rule set contains a default rule that appears directly below the Name option. Find the Name option for that default rule and set it to a name that identifies the purpose of this rule.
5. In the Rule ID option, specify a number between 66,000,000 and 66,999,999.
6. In the Rule message option, type a brief description for this rule.

7. The default rule contains a default condition. Modify this condition to determine how WAF will identify threats.

   1. From the condition's Variable option, select the request element through which WAF will identify threats.

      Learn more about variables.

   2. Certain variables (e.g., request cookies and request header) match on name and value. If you have selected this type of variable, then perform the following steps:

      1. Click + Add Match.

      2. From the Name option, type the desired name.

         For example, match for requests that contain an Authorization header by setting this option to Authorization.

      3. Optional. Mark the Negative Match option to match for requests that do not contain a matching value for the name defined in the previous step.
      4. If you specified a regular expression in the Name option, then you should mark the Regex Match option.
      5. Optional. Add another match through which this variable can be satisfied by repeating steps a - d.

   3. Optional. Mark the Count option to match by the number of instances that a match is found instead of by inspecting that request element.

      Learn more.

   4. Optional. Click + Add Variable to add another variable through which this request may be satisfied. Repeat steps i - iii.

      If you would like to a use a different match value for this variable, then you should create a new rule. Alternatively, if you would like to require both variables prior to threat identification, then you should add it as a new condition to this rule.

   5. From the Operator option, select an operator that determines how WAF will compare the match value to the request element identified by the above variable.

      Learn more.

   6. In the Match value option, type the value that will be compared against the request element identified by the above variable.

   7. From the Match transformations option, select each transformation that will be applied to the source value.

      Learn more.

   8. Optional. Mark the Negative Match option to match for requests that do not contain a matching value for the value defined in step vi.
8. Optional. Click + Add Condition to add another condition that must be met prior to threat identification. Repeat step 7 for this new condition.
9. Optional. Click + Add Rule to add another rule through which WAF may identify threats. Repeat steps 7 and 8.
10. Click Save.

To modify a custom rule set

1. Navigate to the Custom Rules page. How?From the main menu, navigate to More | Security | WAF Tier | Security Rule Manager | Custom Rules.

2. Click on the desired custom rule set.

3. Make the desired changes.

   Key tasks:

   • Delete variables and matches within a variable by clicking .

   • Delete a condition by clicking Delete Condition.

     A rule must have at least one condition. Therefore, you cannot delete the root condition.

   • Delete a rule by clicking Delete Rule and then clicking Confirm.
4. Click Save.

To delete a custom rule set

1. Navigate to the Custom Rules page. How?From the main menu, navigate to More | Security | WAF Tier | Security Rule Manager | Custom Rules.

2. Click on the desired custom rule set.
3. Click Delete Custom Rule Profile.
4. Type DELETE.
5. Click Delete.