When a web application firewall (WAF) is blocking most of the attacks, a direct-to-origin attack is likely to succeed. A direct-to-origin attack targets the backend servers directly, bypassing the WAF. This type of attack exploits any functionality that allows direct access to the origin servers (backend servers) without passing through the WAF. Techniques such as manipulating DNS, exploiting misconfigurations, or using direct IP access can be employed to bypass the WAF, making direct-to-origin attacks effective under these circumstances.
Reference:
OWASP WAF Bypass Techniques
Imperva - What is a WAF? Web Application Firewall