Allocation of Resources Without Limits or Throttling

Summary

Netty's HTTP/3 codec versions from 4.2.0.Final through 4.2.17.Final retains unbounded per-stream QPACK encoder state. "QpackEncoder" stores a queue and a dynamic-table index tracker for every encoded field section that references the QPACK dynamic table, keyed by the peer-controlled QUIC stream ID, and these entries are released only when the remote decoder sends a "Section Acknowledgment" or "Stream Cancellation" instruction not when the HTTP/3 stream completes. There is no limit on the number of tracked streams, field sections, or retained bytes. A remote, unauthenticated HTTP/3 client can advertise a non-zero QPACK dynamic-table capacity, acknowledge the table insertion so the server reuses a dynamically indexed response header, and then omit all mandatory Section Acknowledgments while issuing sequential requests over a single QUIC connection, bypassing concurrent-stream limits and causing unbounded heap growth until the server exhausts memory (Denial-of-Service).