FortiSIEM Rules

Outbound Traffic to Unapproved Public DNS Servers

Rule ID

PH_Rule_PolicyViolation_24

Default Status

Disabled

Description

Detects DNS name resolution via uncommon public DNS servers - Google DNS server is excluded - this is a typical violation of corporate policies. To prevent this rule from creating false positives, make sure that the CMDB Group: Approved Public DNS Server is populated according to corporate policies.

Severity

7

Category

Security

MITRE ATT&CK® Tactics

Policy Violation

MITRE ATT&CK® Techniques

No Technique Specified

Impacts

Application

Data Source

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

Detection

Correlation

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.

600 seconds

Trigger Conditions

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

PublicDNS

SubPattern Definitions

SubPattern Name: PublicDNS

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

destIpPort = 53 AND destIpAddr NOT IN (Group@PH_SYS_NETWORK_PUBLIC_DNS,Group@PH_SYS_NETWORK_ENTERPRISE_INTERNAL_NET,Group@PH_SYS_APP_DNS_SERVER) AND srcIpAddr IN (Group@PH_SYS_NETWORK_ENTERPRISE_INTERNAL_NET) AND eventType IN (Group@PH_SYS_EVENT_PermitNetTraffic, Group@PH_SYS_EVENT_NetflowTraffic, Group@PH_SYS_EVENT_BiNetflowTraffic,Group@PH_SYS_EVENT_CommonDNSTraffic,Group@PH_SYS_EVENT_UncommonDNSTraffic)

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

srcIpAddr

Aggregate Constraint

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

COUNT(*) >= 1

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

 srcIpAddr = PublicDNS.srcIpAddr