Multiple buffer overflows in Doomsday (aka deng) 1.9.0-beta5.1 and earlier allow remote attackers to execute arbitrary code via a long chat (PKT_CHAT) message that is not properly handled by the (1) D_NetPlayerEvent function in d_net.c or the (2) Msg_Write function in net_msg.c, or (3) many commands that are not properly handled by the NetSv_ReadCommands function in d_netsv.c; or (4) cause a denial of service (daemon crash) via a chat (PKT_CHAT) message without a final '\0' character.