The EditingStyle::mergeStyle function in WebKit/Source/core/editing/EditingStyle.cpp in Blink as used in Google Chrome before 53.0.2785.89 on Windows and OS X and before 53.0.2785.92 on Linux mishandles custom properties which allows remote attackers to cause a denial of service or possibly have unspecified other impact via a crafted web site that leverages \type confusion\ in the StylePropertySerializer class.