Heap-based buffer overflow in RealNetworks RealPlayer 11.0 through 11.1, RealPlayer SP 1.0 through 1.1.1, Mac RealPlayer 11.0 through 11.1, and Linux RealPlayer 11.0.2.1744 allows remote attackers to execute arbitrary code via a large Screen Width value in the Screen Descriptor header of a GIF87a file in an RTSP stream.