Unbounded body accumulation in HTTP/3 response loop in hackney

Allocation of Resources Without Limits or Throttling vulnerability in benoitc hackney allows Flooding.

hackney_h3:await_response_loop/6 accumulates the HTTP/3 response body in memory without any size cap. The after Timeout clause is a per-message inactivity timer that resets on every received chunk, housekeeping message, or settings frame — it is not a wall-clock deadline. A malicious HTTP/3 server that emits one small chunk every Timeout - 1 ms with Fin = false and never sends a final frame keeps the loop alive indefinitely while the accumulation buffer grows linearly without bound, eventually exhausting the BEAM process heap and causing an out-of-memory condition.

This issue affects hackney: from 2.0.0 before 4.0.1.

The application must use the HTTP/3 transport by calling hackney_h3 directly or by passing {transport, h3} to hackney:request/5. The default hackney transport (TCP/TLS) is not affected.