Plunk has SSRF via unvalidated AWS SNS SubscriptionConfirmation in POST /webhooks/sns

Plunk is an open-source email platform built on top of AWS SES. Prior to 0.7.0, a Server-Side Request Forgery (SSRF) vulnerability existed in the SNS webhook handler. An unauthenticated attacker could send a crafted request that caused the server to make an arbitrary outbound HTTP GET request to any host accessible from the server. This vulnerability is fixed in 0.7.0.