CDN WAF features

This document details the core features and configurations available within the STACKIT CDN Web Application Firewall feature (CDN WAF).

Feature overview & availability

The following table outlines which CDN WAF features are currently available and which are still being developed:

Feature	API	SDK	Terraform/OpenTofu	Portal
Operating modes	Available	Available	WIP	Available
Tiered offerings	Available	Available	WIP	WIP
Paranoia levels	Available	Available	WIP	WIP
Traffic allow-listing (whitelisting)	Available	Available	WIP	WIP
Hierarchical rule management	Available	Available	WIP	WIP
Managed rule sets	Available	Available	WIP	Available
Custom rules	WIP	WIP	WIP	WIP

CLI support is currently on the roadmap and not yet available.

Base config

To use a CDN WAF it is necessary to have a STACKIT Content Delivery Network (CDN) in place as a base. It is tightly bundled with a CDN as it also works on the edge. Therefore, it is highly recommended to make use of STACKIT CDN features.

Before you can configure CDN WAF properties, you must enable the CDN WAF by setting the mode to ENABLED or LOG_ONLY. If the CDN WAF is not enabled, most properties are not populated.

Operating mode

The operating mode determines how the CDN WAF handles incoming traffic.

Mode	Description
ENABLED	The CDN WAF actively inspects and blocks malicious requests.
LOG_ONLY	The CDN WAF inspects requests and logs matches, but never blocks traffic.
DISABLED	The CDN WAF is completely off. No inspection occurs.

Tier types

You can enable CDN WAF as an additional service within your CDN distribution. For detailed pricing information, see Billing and costs.

• BASIC: Provides standard CDN WAF features and basic rule sets.
• PREMIUM: Unlocks additional premium-only rules and the ability to create custom rules (custom rules are planned for future release).

Premium CDN WAF is deactivated for now, because custom rules are not yet supported.

Paranoia level

The paranoia level defines how aggressively the CDN WAF filters requests. Higher levels are more effective at catching attacks but increase the chance of blocking legitimate traffic (false positives).

Available levels range from least strict to most strict:

• L1 (Lowest chance of false positives)
• L2
• L3
• L4 (Highest chance of false positives)

Whitelists

Whitelists restrict which requests the distribution accepts. The CDN WAF blocks non-whitelisted requests before they reach the origin.

• Allowed HTTP methods: Restricts accepted HTTP methods (e.g., GET, POST, PUT).
• Allowed HTTP versions: Restricts the accepted HTTP protocol versions.
• Allowed request content types: Restricts the accepted Content-Type headers in request bodies (e.g., application/json, multipart/form-data). Formats must be type/subtype without spaces.

Rule management

You control rule behavior using nine properties divided into three specificity groups: collections, rule groups, and rules.

Specificity hierarchy

The rule levels, from broadest to most specific, are:

1. Collections: Broad categories of rules. Currently, the available collections are @builtin/crs/response (response rules) and @builtin/crs/request (request rules).
2. Rule groups: Sub-categories within collections. Call the ListWafCollections operation to view available rule groups.
3. Rules: Individual, specific rules.

Precedence and overrides

The precedence of these levels dictates how overlapping configurations are resolved. The order of precedence is (from highest to lowest):

1. Rule
2. Rule group
3. Collection

This means that a more specific setting always overrides a broader one. For example, disabling a collection but activating a specific rule within it will deactivate every rule in that collection except for the explicitly activated one.

Rule selectors

Use the following properties to enable, disable, or log rules at each hierarchy level:

Level	Enable	Disable	Log-Only
Collections	enabledRuleCollectionIds	disabledRuleCollectionIds	logOnlyRuleCollectionIds
Rule groups	enabledRuleGroupIds	disabledRuleGroupIds	logOnlyRuleGroupIds
Rules	enabledRuleIds	disabledRuleIds	logOnlyRuleIds

Logs

The following log fields are added to the CDN Logs only when an enabled or logged rule is triggered:

Field	Description
Action	The decision made by the CDN WAF regarding the request. Possible values are: Logged: The request is monitored. Blocked: The request is denied. Allowed: The request is permitted.
Timestamp	The exact date and time when the request was made.
Rule	The specific CDN WAF rule that triggered the event. For more information, see Rule collections.
Message	A detailed message describing the CDN WAF event.
URL	The URL of the requested cached resource.
Method	The HTTP method used for the request.
Country	The country where the request originated.
ASN	The Autonomous System Number (ASN) of the network where the request originated.