This vulnerability allows remote attackers to execute arbitrary code on vulnerable installations of Foxit Reader 8.3.1.21155. User interaction is required to exploit this vulnerability in that the target must visit a malicious page or open a malicious file. The specific flaw exists within the handling of references to the app object from FormCalc. The issue results from the lack of proper validation of user-supplied data, which can result in a type confusion condition. An attacker can leverage this to execute code in the context of the current process. Was ZDI-CAN-5072.