This tweet describes a WAF bypass technique using HTTP Parameter Pollution (HPP). The attacker sends a request with duplicated parameters, like user_id=VICTIM and user_id=ATTACKER, causing the server to receive conflicting values. In Node.js applications, type juggling converts parameters into arrays if duplicates exist. Security checks often validate only the first parameter, but backend logic may process the entire array, leading to a bypass of WAF filters. This trick exploits discrepancies between security validation and business logic processing, allowing attackers to circumvent WAF protections by sending duplicated parameters in HTTP requests. The bypass is universal because it targets logical implementation flaws rather than a specific WAF vendor.
For more insights, check out the original tweet here: https://twitter.com/fachrurrozyh028/status/1997937537386758580. And don’t forget to follow @fachrurrozyh028 for more exciting updates in the world of cybersecurity.