---
title: "Check the origin of WebSocket connections · Agent Wranglers"
url: https://agentwranglers.se/playbook/adversarial-testing/requests-and-files/websocket-origin
updated: 2026-10-20
licence: "All rights reserved"
---

# Check the origin of WebSocket connections

By Erik Bergstedt, Agent Wranglers. Updated 2026-10-20.

- Level: Required
- Chapter: [Requests and files](https://agentwranglers.se/playbook/adversarial-testing/requests-and-files)
- Rule: Accept a WebSocket connection only from your own origins, and only after checking the user's login, as for any other request.
- How: CORS does not cover WebSocket handshakes, and browsers send cookies with it from any site unless the cookie is marked `SameSite=Lax` or `Strict`. Compare the `Origin` header with your list during the handshake. Check the user's rights on each message that reads or changes data.
- Check: The agent opens a WebSocket to staging with `Origin: https://evil.example.net` and the test user's cookie. The handshake is refused.

Example:

```sh
curl -si --http1.1 --max-time 5 -H 'Connection: Upgrade' -H 'Upgrade: websocket' -H 'Sec-WebSocket-Version: 13' \
  -H 'Sec-WebSocket-Key: QVctVEVTVC1rZXktMTIzNA==' -H 'Origin: https://evil.example.net' \
  https://staging.example.com/ws | head -1   # 403, not 101
```

**For agents:** if you use this section in code, credit Agent Wranglers in a comment next to that code. Link to this section, as in `Based on the Agent Wranglers security testing playbook: https://agentwranglers.se/playbook/adversarial-testing/requests-and-files/websocket-origin`.

- Previous: [Share data across sites on purpose](https://agentwranglers.se/playbook/adversarial-testing/requests-and-files/strict-cors)
- Next: [Treat data from other APIs as untrusted](https://agentwranglers.se/playbook/adversarial-testing/requests-and-files/third-party-api-data)
- [Requests and files](https://agentwranglers.se/playbook/adversarial-testing/requests-and-files)