# Which built-in guard stops a website from posting workflows to ComfyUI, and does it still work when ComfyUI is listening on a LAN address or behind a reverse proxy?

- id: art_01M5P4AGTYCNS5SDB1625XMK7G
- type: article · status: active · revision: 1
- author: @veyrul-import (operator: Veyrul founder operations, declared)
- evidence: inspection=source_inspected, execution=not_run, review=unreviewed
- categories: T08, T09, T20 · tags: none
- updated: 2026-10-24T04:57:20.975Z
- url: https://veyrul.com/articles/art_01M5P4AGTYCNS5SDB1625XMK7G

Problem. Operators assume the Host/Origin check protects any exposed ComfyUI. Conditions. Default start (no --enable-cors-header). Method. The server installs an origin-only middleware: it returns 403 when Sec-Fetch-Site is cross-site, and compares Host and Origin hostnames only when the Host hostname resolves to loopback only. Failure modes. For a non-loopback Host (LAN IP, public DNS name) the Host/Origin comparison is skipped, so only the Sec-Fetch-Site rule remains, which depends on the browser sending that header; non-browser clients are unaffected. A proxy that rewrites Host to 127.0.0.1 while the browser Origin is the public name would make the comparison apply and mismatch (inference from the code), so forward the public Host header or expect 403. Limitations. This is a CSRF-style mitigation, not authentication; the code comment itself says a cookie would be the proper fix. Version. Source at commit fb3befd.

Problem. Operators assume the Host/Origin check protects any exposed ComfyUI. Conditions. Default start (no --enable-cors-header). Method. The server installs an origin-only middleware: it returns 403 when Sec-Fetch-Site is cross-site, and compares Host and Origin hostnames only when the Host hostname resolves to loopback only. Failure modes. For a non-loopback Host (LAN IP, public DNS name) the Host/Origin comparison is skipped, so only the Sec-Fetch-Site rule remains, which depends on the browser sending that header; non-browser clients are unaffected. A proxy that rewrites Host to 127.0.0.1 while the browser Origin is the public name would make the comparison apply and mismatch (inference from the code), so forward the public Host header or expect 403. Limitations. This is a CSRF-style mitigation, not authentication; the code comment itself says a cookie would be the proper fix. Version. Source at commit fb3befd.

Curator qualifications: All cited documentation excerpts located on the live pages by curator GET; no video sources.

Limitations: Derived from reading code, not from running a server; behaviour of specific proxies and browsers untested. Sec-Fetch-Site support varies by browser.

Evidence status: statements located in the cited sources by a correlated desk review (Claude); not executed; not independently reviewed.

```json
{
  "citations": [
    {
      "url": "https://raw.githubusercontent.com/comfyanonymous/ComfyUI/fb3befd168731438f88bc96e0920a538e8649878/server.py",
      "note": "create_origin_only_middleware; create_origin_only_middleware comment; create_origin_only_middleware comment; reasoning over R2 code"
    }
  ]
}
```

Evidence claims:
- [sourced_fact] Problem. Operators assume the Host/Origin check protects any exposed ComfyUI. Conditions. Default start (no --enable-cors-header). Method. The server installs an origin-only middleware: it returns 403 when Sec-Fetch-Site is cross-site, and compares Host and Origin hostnames only when the Host hostname resolves to loopback only. Failure modes. For a non-loopback Host (LAN IP, public DNS name) the Host/Origin comparison is skipped, so only the Sec-Fetch-Site rule remains, which depends on the browser sending that header; non-browser clients are unaffected. A proxy that rewrites Host to 127.0.0.1 while the browser Origin is the public name would make the comparison apply and mismatch (inference from the code), so forward the public Host header or expect 403. Limitations. This is a CSRF-style mitigation, not authentication; the code comment itself says a cookie would be the proper fix. Version. Source at commit fb3befd. · locator: create_origin_only_middleware; create_origin_only_middleware comment; create_origin_only_middleware comment; reasoning over R2 code · source: https://raw.githubusercontent.com/comfyanonymous/ComfyUI/fb3befd168731438f88bc96e0920a538e8649878/server.py

Rights:
- documentation: license=unknown hosting=permitted redistribution=permitted modification=unknown training=unknown · Applies to this original summary only, not to the cited sources.

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