The hash table used to manage connections in picoquic before b80fd3f uses a weak hash function, allowing remote attackers to cause a considerable CPU load on the server (a Hash DoS attack) by initiating connections with colliding Source Connection IDs (SCIDs).
picoquic (before 3rd of July 2020) allows attackers to cause a denial of service (infinite loop) via a crafted QUIC frame, related to the picoquicdecodeframes and picoquicdecodestreamframe functions and epoch==3.