CVE-2026-86080: n8n: GitHub Trigger 422 Reuse Path Skips Webhook Secret Storage, Causing Signature Verification to Fail-Open

The GitHub Trigger generated a signing secret when it registered a webhook and verified X-Hub-Signature-256 on each delivery. When GitHub answered the create request with a 422 because a webhook for the URL already existed, the node adopted the remote hook but kept only its id and events, discarding the secret it had generated. Deliveries to that workflow’s webhook URL were then accepted from anyone. The patch re-fetches the existing hook by its stored id, re-applies the signing secret, and makes verification fail closed when no secret is stored.