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