This indicates an attack attempt to exploit an Use After Free Vulnerability in Foxit Software PhantomPDF.
The vulnerability is due to an error in the vulnerable application when handling a maliciously crafted PDF file. A remote attacker may be able to exploit this to execute arbitrary code within the context of the application, via a crafted PDF file.
Foxit Software Foxit Reader 18.104.22.16896 and earlier
Foxit Software PhantomPDF 22.214.171.12496 and earlier
System Compromise: Remote attackers can gain control of vulnerable systems.
Apply the most recent upgrade or patch from the vendor: