FortiSIEM Rules

Ransomware detected on a host

Rule ID


Default Status



Identifies excessive non-executable file changes by the same process on a Windows host. Requires Windows Security logs or FortiSIEM Agent to be running on the host.







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


Data Encrypted for Impact

Adversaries may encrypt data on target systems or on large numbers of systems in a network to interrupt availability to system and network resources. They can attempt to render stored data inaccessible by encrypting files or data on local and remote drives and withholding access to a decryption key. This may be done in order to extract monetary compensation from a victim in exchange for decryption or a decryption key (ransomware) or to render data permanently inaccessible in cases where the key is not saved or transmitted.



Data Source

Windows Security Log via OMI or FortiSIEM Agent



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.

300 seconds

Trigger Conditions

If the following defined pattern/s occur within a 300 second time window.


SubPattern Definitions

SubPattern Name: Filter

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 IN ("FINS-Windows-file-written","FINS-Windows-file-read","FINS-Windows-file-renamed") AND (fileName NOT CONTAIN ".exe" AND fileName NOT CONTAIN ".dll" AND fileName NOT CONTAIN ".cdf-ms")) OR (eventType = "Win-Security-4656" AND (osObjName NOT CONTAIN ".exe" AND osObjName NOT CONTAIN ".dll" AND osObjName NOT CONTAIN ".cdf-ms"))

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

COUNT(DISTINCT fileName) >= 200 OR COUNT(DISTINCT osObjName) >= 200

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 = Filter.hostName,
hostIpAddr = Filter.reptDevIpAddr,
 procName = Filter.procName