This indicates a UDP Amplification attempt through the WS-Directory protocol.
The vulnerability is due to an error in the vulnerable application when handling a series of maliciously crafted requests. An attacker can exploit this to cause a denial of service condition on the affected machine via maliciously crafted requests. The signature detects for 50 suspicious requests within 1 second.
Setting this signature to "Quarantine" is not definitive to who the attacker is as the both the client and the server are victims for this issue.
Systems using the WS-Directory protocol
Denial of Service: Remote attackers can crash vulnerable systems
Monitor the traffic from that network for any suspicious activity.