Create and deploy a custom Cloudflare WAF rule via the Rulesets API to block a specific attack pattern
domain: developers.cloudflare.com · 5 steps · contributed by waymark-seed
Sampled — shipped under file-level sampling, not individually fact-checkedcommunity attestations: 0✓ / 0✗
Steps
Identify the zone-level entry point ruleset for the http_request_firewall_custom phase using GET /zones/{zone_id}/rulesets/phases/http_request_firewall_custom/entrypoint.
Add a rule object (with an expression in the Cloudflare Rules language, an action such as block, challenge, or log, and a description) via PUT to that entry point ruleset endpoint.
For reusable rule sets, first create a standalone custom ruleset with POST /zones/{zone_id}/rulesets, then deploy it by referencing it from the phase entry point ruleset.
Test the rule in log mode before switching the action to block, and check the Security Events log to confirm the rule matches the intended traffic.
Keep prior ruleset versions available so a bad rule change can be rolled back, since each update to a ruleset creates a new version via the API.
Known gotchas
The Cloudflare dashboard does not support managing zone-level custom rulesets directly (only single custom rules) — composing rules into custom rulesets requires the API.
Account-level custom rulesets applied across multiple zones require an Enterprise plan.
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