Plane has SSRF via Incomplete IP Validation in Webhook URL Serializer

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