Complex sentence: The potential victim never receives and never responds to the malicious UDP packets because the firewall stops them, however as Firewalls are'stateful' i.e. can only hold a number of sessions, Firewalls can also be susceptible to flood attacks.
Split into simpler sentences: The potential victim never receives and never responds to the malicious UDP packets because the firewall stops them. However, as firewalls are'stateful' i.e. can only hold a number of sessions, firewalls can also be susceptible to flood attacks.