This indicates an attack attempt to exploit a Use After Free Vulnerability in Foxit Software PhantomPDF.
The vulnerability is due to an error in the vulnerable application when handling a maliciously crafted request. A remote attacker may be able to exploit this to execute arbitrary code within the context of the application, via a crafted request.
Foxit Software Foxit Reader 184.108.40.20696 and earlier
Foxit Software PhantomPDF 220.127.116.1196 and earlier
System Compromise: Remote attackers can gain control of vulnerable systems.
Apply the most recent upgrade or patch from the vendor: