Spike in Firewall Deniesedit

A machine learning job detected an unusually large spike in network traffic that was denied by network access control lists (ACLs) or firewall rules. Such a burst of denied traffic is usually caused by either 1) a mis-configured application or firewall or 2) suspicious or malicious activity. Unsuccessful attempts at network transit, in order to connect to command-and-control (C2), or engage in data exfiltration, may produce a burst of failed connections. This could also be due to unusually large amounts of reconnaissance or enumeration traffic. Denial-of-service attacks or traffic floods may also produce such a surge in traffic.

Rule type: machine_learning

Machine learning job: high_count_network_denies

Machine learning anomaly threshold: 75

Severity: low

Risk score: 21

Runs every: 15 minutes

Searches indices from: now-30m (Date Math format, see also Additional look-back time)

Maximum alerts per execution: 100



  • Elastic
  • Network
  • Threat Detection
  • ML

Version: 2 (version history)

Added (Elastic Stack release): 7.13.0

Last modified (Elastic Stack release): 7.14.0

Rule authors: Elastic

Rule license: Elastic License v2

Potential false positivesedit

A misconfgured network application or firewall may trigger this alert. Security scans or test cycles may trigger this alert.

Rule version historyedit

Version 2 (7.14.0 release)
  • Formatting only