FortiSIEM Rules

Sudden Increase in Disk I/O

Rule ID


Default Status



Detects anomaly in disk I/O usage for servers, VMs and ESX hosts - over a 30 minute interval, either the read or write volume is more than 3 standard deviations away from the mean over that same time period and the read/write volume is at least 1 Mbps







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


Endpoint Denial of Service: OS Exhaustion Flood

Adversaries may target the operating system (OS) for a DoS attack, since the (OS) is responsible for managing the finite resources on a system. These attacks do not need to exhaust the actual resources on a system since they can simply exhaust the limits that an OS self-imposes to prevent the entire system from being overwhelmed by excessive demands on its capacity.



Data Source

VCenter Performance Monitoring via VMSDK



Remediation Guidance

Identify the process on the VM that is doing high I/O and determine the root cause.

Time Window

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

1800 seconds

Trigger Conditions

If the following defined pattern/s occur within a 1800 second time window.


SubPattern Definitions

SubPattern Name: StatResource

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


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

((AVG(diskReadKBytesPerSec)-STAT_AVG(AVG(diskReadKBytesPerSec):121))/STAT_STDDEV(AVG(diskReadKBytesPerSec):121) >= 3 AND STAT_STDDEV(AVG(diskReadKBytesPerSec):121) > 0 AND
	  AVG(diskReadKBytesPerSec) >= 1048576) OR
	  ((AVG(diskWriteKBytesPerSec)-STAT_AVG(AVG(diskWriteKBytesPerSec):121))/STAT_STDDEV(AVG(diskWriteKBytesPerSec):121) >= 3 AND STAT_STDDEV(AVG(diskWriteKBytesPerSec):121) > 0 AND
	  AVG(diskWriteKBytesPerSec) >= 1048576)

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

 hostName = StatResource.hostName,
 hostIpAddr = StatResource.hostIpAddr,
 diskName = StatResource.diskName,
 datastore = StatResource.datastore,
 diskReadKBytesPerSec = StatResource.AVG(diskReadKBytesPerSec),
 diskWriteKBytesPerSec = StatResource.AVG(diskWriteKBytesPerSec),
 avgDiskReadKBytesPerSec = StatResource.STAT_AVG(AVG(diskReadKBytesPerSec):121),
 avgDiskWriteKBytesPerSec = StatResource.STAT_AVG(AVG(diskWriteKBytesPerSec):121),
 sdevDiskReadKBytesPerSec = StatResource.STAT_STDDEV(AVG(diskReadKBytesPerSec):121),
 sdevDiskWriteKBytesPerSec = StatResource.STAT_STDDEV(AVG(diskWriteKBytesPerSec):121)