Race condition in the FastCopy optimization in the Array.Copy method in metadata/icall.c in Mono, when Moonlight 2.x before 2.4.1 or 3.x before 3.99.3 is used, allows remote attackers to trigger a buffer overflow and modify internal data structures, and cause a denial of service (plugin crash) or corrupt the internal state of the security manager, via a crafted media file in which a thread makes a change after a type check but before a copy action.