CVE-2025-59348: Dragonfly incorrectly handles a task structure’s usedTrac field

The processPieceFromSource method (figure 4.1) is part of a task processing mechanism. The method writes pieces of data to storage, updating a Task structure along the way. The method does not update the structure’s usedTraffic field, because an uninitialized variable n is used as a guard to the AddTraffic method call, instead of the result.Size variable.

var n int64
result.Size, err = pt.GetStorage().WritePiece([skipped])
result.FinishTime = time.Now().UnixNano()
if n > 0 {
pt.AddTraffic(uint64(n))
}

A task is processed by a peer. The usedTraffic metadata is not updated during the processing. Rate limiting is incorrectly applied, leading to a denial-of-service condition for the peer.