Rare client observed with high reverse DNS lookup count
Id | 15ae38a2-2e29-48f7-883f-863fb25a5a06 |
Rulename | Rare client observed with high reverse DNS lookup count |
Description | Identifies clients with a high reverse DNS counts that could be carrying out reconnaissance or discovery activity. Alerts are generated if the IP performing such reverse DNS lookups was not seen doing so in the preceding 7-day period. |
Severity | Medium |
Tactics | Discovery |
Techniques | T1046 |
Required data connectors | DNS |
Kind | Scheduled |
Query frequency | 1d |
Query period | 8d |
Trigger threshold | 0 |
Trigger operator | gt |
Source Uri | https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/Windows Server DNS/Analytic Rules/DNS_HighReverseDNSCount_detection.yaml |
Version | 1.0.2 |
Arm template | 15ae38a2-2e29-48f7-883f-863fb25a5a06.json |
let starttime = 8d;
let endtime = 1d;
let threshold = 10;
DnsEvents
| where TimeGenerated > ago(endtime)
| where Name has "in-addr.arpa"
| summarize StartTimeUtc = min(TimeGenerated), EndTimeUtc = max(TimeGenerated), dcount(Name), ReverseDNSLookup_List = make_set(Name,100) by ClientIP
| where dcount_Name > threshold
| project StartTimeUtc, EndTimeUtc, ClientIP , dcount_Name, ReverseDNSLookup_List
// Filter out previously seen IPs
// Returns all the records from the left side that don't have matches from the right
| join kind=leftanti (DnsEvents
| where TimeGenerated between(ago(starttime)..ago(endtime))
| where Name has "in-addr.arpa"
| summarize dcount(Name) by ClientIP, bin(TimeGenerated, 1d)
| where dcount_Name > threshold
| project ClientIP , dcount_Name
) on ClientIP
OriginalUri: https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/Windows Server DNS/Analytic Rules/DNS_HighReverseDNSCount_detection.yaml
query: |
let starttime = 8d;
let endtime = 1d;
let threshold = 10;
DnsEvents
| where TimeGenerated > ago(endtime)
| where Name has "in-addr.arpa"
| summarize StartTimeUtc = min(TimeGenerated), EndTimeUtc = max(TimeGenerated), dcount(Name), ReverseDNSLookup_List = make_set(Name,100) by ClientIP
| where dcount_Name > threshold
| project StartTimeUtc, EndTimeUtc, ClientIP , dcount_Name, ReverseDNSLookup_List
// Filter out previously seen IPs
// Returns all the records from the left side that don't have matches from the right
| join kind=leftanti (DnsEvents
| where TimeGenerated between(ago(starttime)..ago(endtime))
| where Name has "in-addr.arpa"
| summarize dcount(Name) by ClientIP, bin(TimeGenerated, 1d)
| where dcount_Name > threshold
| project ClientIP , dcount_Name
) on ClientIP
description: |
'Identifies clients with a high reverse DNS counts that could be carrying out reconnaissance or discovery activity.
Alerts are generated if the IP performing such reverse DNS lookups was not seen doing so in the preceding 7-day period.'
severity: Medium
requiredDataConnectors:
- dataTypes:
- DnsEvents
connectorId: DNS
name: Rare client observed with high reverse DNS lookup count
triggerThreshold: 0
tactics:
- Discovery
version: 1.0.2
relevantTechniques:
- T1046
triggerOperator: gt
entityMappings:
- entityType: IP
fieldMappings:
- columnName: ClientIP
identifier: Address
id: 15ae38a2-2e29-48f7-883f-863fb25a5a06
status: Available
kind: Scheduled
queryFrequency: 1d
queryPeriod: 8d
{
"$schema": "https://schema.management.azure.com/schemas/2019-04-01/deploymentTemplate.json#",
"contentVersion": "1.0.0.0",
"parameters": {
"workspace": {
"type": "String"
}
},
"resources": [
{
"apiVersion": "2024-01-01-preview",
"id": "[concat(resourceId('Microsoft.OperationalInsights/workspaces/providers', parameters('workspace'), 'Microsoft.SecurityInsights'),'/alertRules/15ae38a2-2e29-48f7-883f-863fb25a5a06')]",
"kind": "Scheduled",
"name": "[concat(parameters('workspace'),'/Microsoft.SecurityInsights/15ae38a2-2e29-48f7-883f-863fb25a5a06')]",
"properties": {
"alertRuleTemplateName": "15ae38a2-2e29-48f7-883f-863fb25a5a06",
"customDetails": null,
"description": "'Identifies clients with a high reverse DNS counts that could be carrying out reconnaissance or discovery activity.\nAlerts are generated if the IP performing such reverse DNS lookups was not seen doing so in the preceding 7-day period.'\n",
"displayName": "Rare client observed with high reverse DNS lookup count",
"enabled": true,
"entityMappings": [
{
"entityType": "IP",
"fieldMappings": [
{
"columnName": "ClientIP",
"identifier": "Address"
}
]
}
],
"OriginalUri": "https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/Windows Server DNS/Analytic Rules/DNS_HighReverseDNSCount_detection.yaml",
"query": "let starttime = 8d;\nlet endtime = 1d;\nlet threshold = 10;\nDnsEvents\n| where TimeGenerated > ago(endtime)\n| where Name has \"in-addr.arpa\"\n| summarize StartTimeUtc = min(TimeGenerated), EndTimeUtc = max(TimeGenerated), dcount(Name), ReverseDNSLookup_List = make_set(Name,100) by ClientIP\n| where dcount_Name > threshold\n| project StartTimeUtc, EndTimeUtc, ClientIP , dcount_Name, ReverseDNSLookup_List\n// Filter out previously seen IPs\n// Returns all the records from the left side that don't have matches from the right\n| join kind=leftanti (DnsEvents\n | where TimeGenerated between(ago(starttime)..ago(endtime))\n | where Name has \"in-addr.arpa\"\n | summarize dcount(Name) by ClientIP, bin(TimeGenerated, 1d)\n | where dcount_Name > threshold\n | project ClientIP , dcount_Name\n) on ClientIP\n",
"queryFrequency": "P1D",
"queryPeriod": "P8D",
"severity": "Medium",
"status": "Available",
"subTechniques": [],
"suppressionDuration": "PT1H",
"suppressionEnabled": false,
"tactics": [
"Discovery"
],
"techniques": [
"T1046"
],
"templateVersion": "1.0.2",
"triggerOperator": "GreaterThan",
"triggerThreshold": 0
},
"type": "Microsoft.OperationalInsights/workspaces/providers/alertRules"
}
]
}