Webhook Security's Blind Spot: Why Delivery Workers Are Your Riskiest Component

Most webhook security efforts focus on verifying inbound payloads, but the real threat lives in the delivery worker—the outbound HTTP client that posts events to customer URLs. DNS rebinding attacks can redirect these requests to internal cloud metadata endpoints like 169.254.169.254, potentially leaking critical IAM credentials. This architecture vulnerability cannot be fixed by HMAC signatures alone; every outbound request must validate DNS resolution and private IP ranges at delivery time, not just registration.