GHSA-fpx8-73gf-7x73

### Summary The webhook URL validation in `plane/app/serializers/webhook.py` only checks `ip.is_loopback`, allowing attackers with workspace ADMIN role to create webhooks pointing to private/internal network addresses (`10.x.x.x`, `172.16.x.x`, `192.168.x.x`, `169.254.169.254`, etc.). When webhook events fire, the server makes requests to these internal addresses and stores the response — enabling SSRF with full response read-back. ### Impact - **Cloud metadata exfiltration**: Access AWS/GCP/Azure instance metadata (IAM credentials, tokens) - **Internal service scanning**: Probe internal network services not exposed to the internet - **Data exfiltration via response logs**: Full response body from internal services is stored and returned to the attacker through the webhook logs API - Bypass vectors: `10.0.0.0/8`, `172.16.0.0/12`, `192.168.0.0/16`, `169.254.0.0/16`, `0.0.0.0`, `::ffff:` mapped addresses