---
description: Block or restrict Worker subrequests from other Cloudflare zones.
title: Block Worker subrequests from other zones
image: https://developers.cloudflare.com/waf/custom-rules/use-cases/block-worker-subrequests/og.png?v=5caf44ada9087388
---

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# Block Worker subrequests from other zones

Last updated Oct 5, 2026|Copy as Markdown| [View as Markdown](https://developers.cloudflare.com/waf/custom-rules/use-cases/block-worker-subrequests/index.md)| [Agent setup](https://developers.cloudflare.com/agent-setup/)

The [`cf.worker.upstream_zone`](https://developers.cloudflare.com/ruleset-engine/rules-language/fields/reference/cf.worker.upstream_zone/) field identifies the zone that spawned a [Workers subrequest](https://developers.cloudflare.com/workers/platform/limits/#subrequests). You can use this field in [custom rules](https://developers.cloudflare.com/waf/custom-rules/) to mitigate unwanted Worker traffic.

Caution

Do not use the [`CF-Worker`](https://developers.cloudflare.com/fundamentals/reference/http-headers/#cf-worker) request header in WAF rules. The header is added after rule evaluation, so it is not available when WAF rules run. Use the `cf.worker.upstream_zone` field instead, which holds the same value.

### Block subrequests from a specific zone

- **When incoming requests match**:

  If you are using the expression editor:  
  `(cf.worker.upstream_zone eq "example.com")`
- **Then take action**: *Block*

### Block all Worker subrequests except from your own zone

- **When incoming requests match**:

  If you are using the expression editor:  
  `(not cf.worker.upstream_zone in {"" "your-zone.com"})`
- **Then take action**: *Block*

The empty string matches requests that did not come from a Worker, so this expression only blocks subrequests from other zones. Direct visitor traffic is not affected.

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