Methods, non-transitory computer readable media, protection server apparatuses, and network security systems that improve network security for web applications by mitigating cyberattacks that cause the exfiltration of data are illustrated. With this technology, network request(s) are received from a client that specify domain(s) to which the client has sent data during rendering of a webpage. The webpage includes instrumentation code configured to intercept and post the network requests. A determination is then mage when one of the domain(s) is a malicious domain. Interceptor code is generated based on a type of attack that is associated with the one of the domains, when the determination indicates the one of the domains is a malicious domain. The instrumentation code is then updated to include the interceptor code. The interceptor code is configured to mitigate the attack when the webpage is subsequently rendered by another client.