Ubiquiti - Unusual DNS connection

Status: available
Severity: medium
Time window: 1h
Group by: DstIpAddr, SrcIpAddr
Source: github.com/Azure/Azure-Sentinel

'Detects unusual remote to local (R2L) DNS connections.'

MITRE ATT&CK coverage

Tactic	Techniques
Command & Control	`T1090` Proxy `T1572` Protocol Tunneling

Rule body

id: 14a23ded-7fb9-48ee-ba39-859517a49b51
name: Ubiquiti - Unusual DNS connection
description: |
  'Detects unusual remote to local (R2L) DNS connections.'
severity: Medium
status: Available
requiredDataConnectors:
  - connectorId: CustomLogsAma
    dataTypes:
      - Ubiquiti_CL
queryFrequency: 1h
queryPeriod: 1h
triggerOperator: gt
triggerThreshold: 0
tactics:
  - CommandAndControl
relevantTechniques:
  - T1090
  - T1572
query: |
  let threshold = 50;
  UbiquitiAuditEvent
  | where EventCategory =~ 'firewall'
  | where ipv4_is_private(SrcIpAddr) == 'False'
  | where ipv4_is_private(DstIpAddr)
  | where DstPortNumber == '53'
  | summarize count() by SrcIpAddr, DstIpAddr
  | where count_ > threshold
  | extend IPCustomEntity = DstIpAddr
entityMappings:
  - entityType: IP
    fieldMappings:
      - identifier: Address
        columnName: IPCustomEntity
version: 1.0.2
kind: Scheduled

Stages and Predicates

Parameters

let threshold = 50;

Stage 1: `source`

UbiquitiAuditEvent

Stage 2: `where`

| where EventCategory =~ 'firewall'

Stage 3: `where`

| where ipv4_is_private(SrcIpAddr) == 'False'

Stage 4: `where`

| where ipv4_is_private(DstIpAddr)

Stage 5: `where`

| where DstPortNumber == '53'

Stage 6: `summarize`

| summarize count() by SrcIpAddr, DstIpAddr

Stage 7: `where`

| where count_ > threshold

Stage 8: `extend`

| extend IPCustomEntity = DstIpAddr

Exclusions

The rule actively suppresses these predicates.

Field	Kind	Excluded values	Search
`SrcIpAddr`	cidr_match	`10.0.0.0/8`, `172.16.0.0/12`, `192.168.0.0/16`, `169.254.0.0/16`, `127.0.0.0/8`	`excludes:SrcIpAddr`

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`DstIpAddr`	cidr_match	`10.0.0.0/8` `127.0.0.0/8` `169.254.0.0/16` `172.16.0.0/12` `192.168.0.0/16`	`field:"dest_ip" kind:cidr_match`
`DstPortNumber`	eq	`53`	`field:"DstPortNumber" kind:eq value:"53"`
`EventCategory`	eq	`firewall`	`field:"EventCategory" kind:eq value:"firewall"`
`count_`	gt	`50`	`field:"count_" kind:gt value:"50"`

Output fields

These fields are emitted when the rule matches.

Field	Source
`DstIpAddr`	`summarize`
`SrcIpAddr`	`summarize`
`IPCustomEntity`	`extend`

Ubiquiti - Unusual DNS connection

MITRE ATT&CK coverage

Rule body

Stages and Predicates

Parameters

Stage 1: source

Stage 2: where

Stage 3: where

Stage 4: where

Stage 5: where

Stage 6: summarize

Stage 7: where

Stage 8: extend