This indicates an attack attempt to exploit a Use After Free Vulnerability in Nitro PDF Nitro Pro.
This vulnerability is due to improper handling of page objects. A remote attacker could exploit this vulnerability by enticing a user to open a crafted PDF document. Successful exploitation could allow the attacker to execute arbitrary code in the context of the application.
Nitro PDF Nitro Pro 188.8.131.52
System Compromise: Remote attackers can gain control of vulnerable systems.
Apply the most recent upgrade or patch from the vendor.