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.

Affected: Hex: hackney

### Summary

`hackney_h3:await_response_loop/6` in `src/hackney_h3.erl` accumulates the HTTP/3 response body in memory without any size cap. The `after Timeout` clause is a per-message inactivity timer, not a wall-clock deadline: every received `stream_data` chunk, housekeeping `select` message, or `settings` frame resets it. A malicious HTTP/3 server that drips one small chunk every `Timeout - 1` ms with `Fin = false` and never terminates the stream keeps the loop alive indefinitely while the accumulation buffer grows without bound, eventually exhausting the BEAM process heap.

### Details

In `src/hackney_h3.erl`, `await_response_loop/6` (line 430) builds the body with:

```erlang NewBody = <<AccBody/binary, Data/binary>> ```

There is no `max_body` check and no monotonic deadline. The `after Timeout` clause at line 463 is restarted on each loop iteration. A server that ensures at least one message arrives within `Timeout` ms indefinitely (one small chunk per interval is sufficient) prevents the timeout from firing while `AccBody` grows linearly. The same module's `wait_connected/3` (lines 388-389) shows the correct pattern: track an absolute start time and pass a shrinking `Remaining` budget into each `receive`. This loop does not.

### Configurations

Only the HTTP/3 transport is affected. Applications using the default TCP/TLS hackney transport are not vulnerable. The vulnerability requires using `hackney_h3` directly or passing `{transport, h3}` to `hackney:request/5`.…