Local code execution via malformed NaN parsing

Heap buffer overflow in sheredom json.h before commit 0825301 allows local users to execute arbitrary code through crafted JSON. The size pass accepts an E after a NaN token, causing json_parse_value to receive an out-of-bounds value pointer and perform an eight-byte heap write. Exploitation requires an application to invoke json_parse_ex with the vulnerable flag combination on attacker-controlled JSON; the resulting memory corruption can execute code with that application's privileges.