End User DNS Queries to Unauthorized DNS Servers

Rule ID

PH_Rule_Flow_12

Default Status

Enabled

Description

Detects a scenario where a host, that is itself not a DNS server, is trying to send DNS requests to unauthorized DNS servers. Authorized DNS servers are represented by the "DNS Server" group. In a typical scenario, end hosts always send DNS requests to authorized DNS servers which in turn communicate to other DNS servers - so this behavior may indicate malware running on the end host.

Severity

MITRE ATT&CK® Tactics

Command And Control

MITRE ATT&CK® Techniques

T1568.001

Dynamic Resolution: Fast Flux DNS

Adversaries may use Fast Flux DNS to hide a command and control channel behind an array of rapidly changing IP addresses linked to a single domain resolution. This technique uses a fully qualified domain name, with multiple IP addresses assigned to it which are swapped with high frequency, using a combination of round robin IP addressing and short Time-To-Live (TTL) for a DNS resource record.

https://attack.mitre.org/techniques/T1568/001

Impacts

Network

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.

300 seconds

Trigger Conditions

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

UnauthDNS

SubPattern Definitions

SubPattern Name: UnauthDNS

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

ipProto = 17 AND destIpPort = 53 AND destIpAddr NOT IN (Group@PH_SYS_APP_DNS_SERVER) AND destIpAddr NOT IN (Group@PH_SYS_NETWORK_PUBLIC_DNS) AND srcIpAddr NOT IN (Group@PH_SYS_APP_DNS_SERVER,Group@PH_SYS_APP_ACCELOPS,Group@PH_SYS_DEVICE_FSM) 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_DenyNetTraffic)

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 (DISTINCT destIpAddr) >= 10

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 = UnauthDNS.srcIpAddr,
 incidentCount = UnauthDNS.COUNT (DISTINCT destIpAddr)

FortiSIEM Rules