This indicates an attack attempt to exploit a Arbitrary File Upload vulnerability in WordPress plugin wp-database-backup.
The vulnerability is due to insufficient sanitizing of user supplied inputs in the application when handling a craft HTTP request. An authenticated remote attacker may be able exploit this to execute arbitrary code within the context of the application.
WordPress plugin wp-database-backup prior to version 5.2
System Compromise: Remote attackers can gain control of vulnerable systems.
Upgrade to latest version from the vendor.