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
entityMappings:
- entityType: IP
fieldMappings:
- identifier: Address
columnName: ClientIP
name: Rare client observed with high reverse DNS lookup count
tactics:
- Discovery
severity: Medium
triggerThreshold: 0
relevantTechniques:
- T1046
id: 15ae38a2-2e29-48f7-883f-863fb25a5a06
version: 1.0.2
OriginalUri: https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/Windows Server DNS/Analytic Rules/DNS_HighReverseDNSCount_detection.yaml
queryFrequency: 1d
triggerOperator: gt
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.'
requiredDataConnectors:
- connectorId: DNS
dataTypes:
- DnsEvents
status: Available
queryPeriod: 8d
kind: Scheduled
{
"$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"
}
]
}