FortiSIEM Rules

IIS Virtual Memory Critical

Rule ID


Default Status



Detects that IIS is using at least 1.9 GB of virtual memory and is fast approaching the 2 GB limit.







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: Application Exhaustion Flood

Adversaries may target resource intensive features of web applications to cause a denial of service (DoS). Specific features in web applications may be highly resource intensive. Repeated requests to those features may be able to exhaust system resources and deny access to the application or the server itself.



Data Source

Microsoft IIS Performance Monitoring via OMI/Agent



Remediation Guidance

Determine why IIS is using so much memory

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: IISVMWarn

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_PROC_RESOURCE_UTIL" AND appName = "Microsoft IIS"

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(virtMemKBytes) >= 1900000  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 = IISVMWarn.hostIpAddr,
 hostName = IISVMWarn.hostName,
 virtMemKBytes = IISVMWarn.AVG(virtMemKBytes)