The Lithtech engine, as used in (1) Contract Jack 1.1 and earlier, (2) No one lives forever 2 1.3 and earlier, (3) Tron 2.0 1.042 and earlier, (4) F.E.A.R. (First Encounter Assault and Recon), and possibly other games, allows remote attackers to cause a denial of service (connection refused) via a UDP packet that causes recvfrom to generate a return code that causes the listening loop to exit, as demonstrated using zero byte packets or packets between 8193 and 12280 bytes, which result in conditions that are not "Operation would block."