The multiplayer engine in Wesnoth 1.2.x before 1.2.7 and 1.3.x before 1.3.9 allows remote servers to cause a denial of service (crash) via a long message with multibyte characters that can produce an invalid UTF-8 string after it is truncated, which triggers an uncaught exception, involving the truncate_message function in server/server.cpp.  NOTE: this issue affects both clients and servers.