FortiSIEM Rules

Sudden Increase In Permitted Traffic To Host

Rule ID


Default Status



Detects traffic anomaly to a destination. This means that the permitted traffic pattern to the destination is statistically anomalous in the following sense: over a 15 minute time window, at least 500 permitted flows and excessive traffic, peers or ports. Excessive traffic is detected from the number of permitted flows destined to this host and total exchanged bytes more than three standard deviations away from mean for the current hour. Excessive peers amounts to more than twice the statistical average for the current hour. Excessive destination ports amounts to more than five times the statistical average for the current hour.







Impact consists of techniques that adversaries use to disrupt availability or compromise integrity by manipulating business and operational processes. Techniques used for impact can include destroying or tampering with data. In some cases, business processes can look fine, but may have been altered to benefit the adversaries’ goals. These techniques might be used by adversaries to follow through on their end goal or to provide cover for a confidentiality breach.

MITRE ATT&CK® Techniques


Network Denial of Service: Direct Network Flood

Adversaries may attempt to cause a denial of service (DoS) by directly sending a high-volume of network traffic to a target. Almost any network protocol may be used for flooding. Stateless protocols such as UDP or ICMP are commonly used but stateful protocols such as TCP can be used as well. Botnets are commonly used to conduct network flooding attacks against networks and services. Large botnets can generate a significant amount of traffic from systems spread across the global Internet. In some of the worst cases for distributed DoS (DDoS), so many systems are used to generate the flood that each one only needs to send out a small amount of traffic to produce enough volume to saturate the target network. In such circumstances, distinguishing DDoS traffic from legitimate clients becomes exceedingly difficult.



Data Source

FortiGate via Syslog or Netflow, Cisco IOS via Syslog or Netflow, Checkpoint via Syslog or Netflow, Palo Alto via Syslog or Netflow



Remediation Guidance

No remediation guidance specified

Time Window

If the following pattern or patterns match an ingested event within the given time window in seconds, trigger an incident.

900 seconds

Trigger Conditions

If the following defined pattern/s occur within a 900 second time window.


SubPattern Definitions

SubPattern Name: StatHighFlowToDest

This is the named definition of the event query, this is important if multiple subpatterns are defined to distinguish them.

SubPattern Query

This is the query logic that matches incoming events

(ipProto = 17 OR ipProto = 6) AND
          eventType IN (Group@PH_SYS_EVENT_PermitNetTraffic, Group@PH_SYS_EVENT_NetflowTraffic, Group@PH_SYS_EVENT_BiNetflowTraffic) AND

Group by Attributes

This defines how matching events are aggregated, only events with the same matching attribute values are grouped into one unique incident ID


Aggregate Constraint

This is most typically a numerical constraint that defines when the rule should trigger an incident

SUM(totFlows) >= 500 AND
	   ((SUM(totFlows)-STAT_AVG(SUM(totFlows):126))/STAT_STDDEV(SUM(totFlows):126) >= 3 AND
           (SUM(totBytes64)-STAT_AVG(SUM(totBytes64):126))/STAT_STDDEV(SUM(totBytes64):126) >= 3 AND
	   STAT_STDDEV(SUM(totFlows):126) > 0 AND STAT_STDDEV(SUM(totBytes64):126)> 0)

Incident Attribute Mapping

This section defines which fields in matching raw events should be mapped to the incident attributes in the resulting incident.

The available raw event attributes to map are limited to the group by attributes and the aggregate event constraint fields for each subpattern

 destIpAddr = StatHighFlowToDest.destIpAddr,
 totFlows = StatHighFlowToDest.SUM(totFlows),
 totBytes64 = StatHighFlowToDest.SUM(totBytes64),
 avgTotFlows = StatHighFlowToDest.STAT_AVG(SUM(totFlows):126),
 sdevTotFlows = StatHighFlowToDest.STAT_STDDEV(SUM(totFlows):126),
 avgTotBytes64 = StatHighFlowToDest.STAT_AVG(SUM(totBytes64):126),
 sdevTotBytes64 = StatHighFlowToDest.STAT_STDDEV(SUM(totBytes64):126)