The issue is related to errors in the mechanism controlling resource expenditure in HTTP/2 implementations, potentially leading to a denial of service. An attacker can exploit this by opening the HTTP/2 window, allowing the peer to send without constraint, while keeping the TCP window closed, preventing the peer from writing bytes on the wire. The attacker then sends a stream of requests for a large response object, which can consume excess memory, CPU, or both, depending on how servers queue responses.