This indicates an attack attempt against a Denial of Service vulnerability in OpenVPN.
The vulnerability is caused by an error when the vulnerable software handles maliciously crafted packets. A remote attacker may be able to exploit this to cause a denial of service condition on the affected system, via a crafted packet.
OpenVPN Project OpenVPN prior to 2.4.2
OpenVPN Project OpenVPN prior to 2.3.15
Denial of Service: Remote attacker can crash vulnerable systems.
Apply the most recent upgrade or patch from the vendor.