FortiSIEM Rules

Virtual Machine CPU Critical

Rule ID


Default Status



Detects that virtual server CPU ready percent has reached a critical level (greater than 25% based on 2 successive readings in a 10 minute interval







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 or ESX via VM_SDK



Remediation Guidance

VM CPU Ready is a measure of the time a VM has to wait for CPU resources from the host. VMware recommends CPU ready should be less than 5%. If the ready time values are high on the VM that experience bad performance, then check for CPU limiting: Make sure the VM is not constrained by a CPU limit set by itself. Make sure that the VM is not constrained by its resource pool. If there is no CPU limiting, then the host could be too oversubscribed.

Time Window

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

600 seconds

Trigger Conditions

If the following defined pattern/s occur within a 600 second time window.


SubPattern Definitions

SubPattern Name: VMCPUHigh

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

eventType = "PH_DEV_MON_VM_CPU_UTIL"

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(cpuReadyPct) >= DeviceToCMDBAttr(hostIpAddr,ReadyCPUPctThreshCrit) AND COUNT(*) >= 2

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

 hostIpAddr = VMCPUHigh.hostIpAddr,
hostName = VMCPUHigh.hostName,
phyMachIpAddr = VMCPUHigh.phyMachIpAddr,
phyMachName = VMCPUHigh.phyMachName,
cpuReadyPct = VMCPUHigh.AVG(cpuReadyPct),
vmName = VMCPUHigh.vmName,
relayDevIpAddr = VMCPUHigh.relayDevIpAddr