X.org libXtst before 1.2.3 allows remote X servers to cause a denial of service (infinite loop) via a reply in the (1) XRecordStartOfData, (2) XRecordEndOfData, or (3) XRecordClientDied category without a client sequence and with attached data.
https://lists.x.org/archives/xorg-announce/2016-October/002720.html
https://cgit.freedesktop.org/xorg/lib/libXtst/commit/?id=9556ad67af3129ec4a7a4f4b54a0d59701beeae3
http://www.securitytracker.com/id/1036945
http://www.securityfocus.com/bid/93375