Detect Abnormal Deny Rate for Source to Destination IP

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Id	e3b6a9e7-4c3a-45e6-8baf-1d3bfa8e0c2b
Rulename	Detect Abnormal Deny Rate for Source to Destination IP
Description	Identifies abnormal deny rate for specific source IP to destination IP based on the normal average and standard deviation learned during a configured period. This can indicate potential exfiltration, initial access, or C2, where an attacker tries to exploit the same vulnerability on machines in the organization but is being blocked by firewall rules.
Severity	Medium
Tactics	InitialAccess Exfiltration CommandAndControl
Required data connectors	AzureActiveDirectory
Kind	Scheduled
Query frequency	1h
Query period	25h
Trigger threshold	1
Trigger operator	gt
Source Uri	https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/Global Secure Access/Analytic Rules/SWG - Abnormal Deny Rate.yaml
Version	1.0.0
Arm template	e3b6a9e7-4c3a-45e6-8baf-1d3bfa8e0c2b.json

KQL

let NumOfStdsThreshold = 3;
let LearningPeriod = 5d;
let BinTime = 1h;
let MinThreshold = 5.0;
let MinLearningBuckets = 5;
let TrafficLogs = NetworkAccessTraffic
  | where Action == 'Denied'
  | where isnotempty(DestinationIp) and isnotempty(SourceIp);
let LearningSrcIpDenyRate = TrafficLogs
  | where TimeGenerated between (ago(LearningPeriod + 1d) .. ago(1d))
  | summarize count() by SourceIp, bin(TimeGenerated, BinTime), DestinationIp
  | summarize LearningTimeSrcIpDenyRateAvg = avg(count_), LearningTimeSrcIpDenyRateStd = stdev(count_), LearningTimeBuckets = count() by SourceIp, DestinationIp
  | where LearningTimeBuckets > MinLearningBuckets;
let AlertTimeSrcIpDenyRate = TrafficLogs
  | where TimeGenerated between (ago(1h) .. now())
  | summarize AlertTimeSrcIpDenyRateCount = count() by SourceIp, DestinationIp;
AlertTimeSrcIpDenyRate
  | join kind=leftouter (LearningSrcIpDenyRate) on SourceIp, DestinationIp
  | extend LearningThreshold = max_of(LearningTimeSrcIpDenyRateAvg + NumOfStdsThreshold * LearningTimeSrcIpDenyRateStd, MinThreshold)
  | where AlertTimeSrcIpDenyRateCount > LearningThreshold
  | project SourceIp, DestinationIp, AlertTimeSrcIpDenyRateCount, LearningThreshold

YAML

query: |
  let NumOfStdsThreshold = 3;
  let LearningPeriod = 5d;
  let BinTime = 1h;
  let MinThreshold = 5.0;
  let MinLearningBuckets = 5;
  let TrafficLogs = NetworkAccessTraffic
    | where Action == 'Denied'
    | where isnotempty(DestinationIp) and isnotempty(SourceIp);
  let LearningSrcIpDenyRate = TrafficLogs
    | where TimeGenerated between (ago(LearningPeriod + 1d) .. ago(1d))
    | summarize count() by SourceIp, bin(TimeGenerated, BinTime), DestinationIp
    | summarize LearningTimeSrcIpDenyRateAvg = avg(count_), LearningTimeSrcIpDenyRateStd = stdev(count_), LearningTimeBuckets = count() by SourceIp, DestinationIp
    | where LearningTimeBuckets > MinLearningBuckets;
  let AlertTimeSrcIpDenyRate = TrafficLogs
    | where TimeGenerated between (ago(1h) .. now())
    | summarize AlertTimeSrcIpDenyRateCount = count() by SourceIp, DestinationIp;
  AlertTimeSrcIpDenyRate
    | join kind=leftouter (LearningSrcIpDenyRate) on SourceIp, DestinationIp
    | extend LearningThreshold = max_of(LearningTimeSrcIpDenyRateAvg + NumOfStdsThreshold * LearningTimeSrcIpDenyRateStd, MinThreshold)
    | where AlertTimeSrcIpDenyRateCount > LearningThreshold
    | project SourceIp, DestinationIp, AlertTimeSrcIpDenyRateCount, LearningThreshold      
id: e3b6a9e7-4c3a-45e6-8baf-1d3bfa8e0c2b
name: Detect Abnormal Deny Rate for Source to Destination IP
severity: Medium
triggerThreshold: 1
description: |
    Identifies abnormal deny rate for specific source IP to destination IP based on the normal average and standard deviation learned during a configured period. This can indicate potential exfiltration, initial access, or C2, where an attacker tries to exploit the same vulnerability on machines in the organization but is being blocked by firewall rules.
status: Available
relevantTechniques: []
triggerOperator: gt
tactics:
- InitialAccess
- Exfiltration
- CommandAndControl
entityMappings:
- fieldMappings:
  - columnName: SourceIp
    identifier: Address
  entityType: IP
- fieldMappings:
  - columnName: DestinationIp
    identifier: Url
  entityType: URL
requiredDataConnectors:
- connectorId: AzureActiveDirectory
  dataTypes:
  - NetworkAccessTrafficLogs
kind: Scheduled
configurableParameters:
- minimumOfStdsThreshold: The number of stds to use in the threshold calculation. Default is set to 3.
- learningPeriodTime: Learning period for threshold calculation in days. Default is set to 5.
- binTime: Learning buckets time in hours. Default is set to 1 hour.
- minimumThreshold: Minimum threshold for alert. Default is set to 5.
- minimumBucketThreshold: Minimum learning buckets threshold for alert. Default is set to 5.
queryPeriod: 25h
queryFrequency: 1h
version: 1.0.0
OriginalUri: https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/Global Secure Access/Analytic Rules/SWG - Abnormal Deny Rate.yaml

ARM

{
  "$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/e3b6a9e7-4c3a-45e6-8baf-1d3bfa8e0c2b')]",
      "kind": "Scheduled",
      "name": "[concat(parameters('workspace'),'/Microsoft.SecurityInsights/e3b6a9e7-4c3a-45e6-8baf-1d3bfa8e0c2b')]",
      "properties": {
        "alertRuleTemplateName": "e3b6a9e7-4c3a-45e6-8baf-1d3bfa8e0c2b",
        "configurableParameters": [
          {
            "minimumOfStdsThreshold": "The number of stds to use in the threshold calculation. Default is set to 3."
          },
          {
            "learningPeriodTime": "Learning period for threshold calculation in days. Default is set to 5."
          },
          {
            "binTime": "Learning buckets time in hours. Default is set to 1 hour."
          },
          {
            "minimumThreshold": "Minimum threshold for alert. Default is set to 5."
          },
          {
            "minimumBucketThreshold": "Minimum learning buckets threshold for alert. Default is set to 5."
          }
        ],
        "customDetails": null,
        "description": "Identifies abnormal deny rate for specific source IP to destination IP based on the normal average and standard deviation learned during a configured period. This can indicate potential exfiltration, initial access, or C2, where an attacker tries to exploit the same vulnerability on machines in the organization but is being blocked by firewall rules.\n",
        "displayName": "Detect Abnormal Deny Rate for Source to Destination IP",
        "enabled": true,
        "entityMappings": [
          {
            "entityType": "IP",
            "fieldMappings": [
              {
                "columnName": "SourceIp",
                "identifier": "Address"
              }
            ]
          },
          {
            "entityType": "URL",
            "fieldMappings": [
              {
                "columnName": "DestinationIp",
                "identifier": "Url"
              }
            ]
          }
        ],
        "OriginalUri": "https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/Global Secure Access/Analytic Rules/SWG - Abnormal Deny Rate.yaml",
        "query": "let NumOfStdsThreshold = 3;\nlet LearningPeriod = 5d;\nlet BinTime = 1h;\nlet MinThreshold = 5.0;\nlet MinLearningBuckets = 5;\nlet TrafficLogs = NetworkAccessTraffic\n  | where Action == 'Denied'\n  | where isnotempty(DestinationIp) and isnotempty(SourceIp);\nlet LearningSrcIpDenyRate = TrafficLogs\n  | where TimeGenerated between (ago(LearningPeriod + 1d) .. ago(1d))\n  | summarize count() by SourceIp, bin(TimeGenerated, BinTime), DestinationIp\n  | summarize LearningTimeSrcIpDenyRateAvg = avg(count_), LearningTimeSrcIpDenyRateStd = stdev(count_), LearningTimeBuckets = count() by SourceIp, DestinationIp\n  | where LearningTimeBuckets > MinLearningBuckets;\nlet AlertTimeSrcIpDenyRate = TrafficLogs\n  | where TimeGenerated between (ago(1h) .. now())\n  | summarize AlertTimeSrcIpDenyRateCount = count() by SourceIp, DestinationIp;\nAlertTimeSrcIpDenyRate\n  | join kind=leftouter (LearningSrcIpDenyRate) on SourceIp, DestinationIp\n  | extend LearningThreshold = max_of(LearningTimeSrcIpDenyRateAvg + NumOfStdsThreshold * LearningTimeSrcIpDenyRateStd, MinThreshold)\n  | where AlertTimeSrcIpDenyRateCount > LearningThreshold\n  | project SourceIp, DestinationIp, AlertTimeSrcIpDenyRateCount, LearningThreshold    \n",
        "queryFrequency": "PT1H",
        "queryPeriod": "PT25H",
        "severity": "Medium",
        "status": "Available",
        "subTechniques": [],
        "suppressionDuration": "PT1H",
        "suppressionEnabled": false,
        "tactics": [
          "CommandAndControl",
          "Exfiltration",
          "InitialAccess"
        ],
        "techniques": [],
        "templateVersion": "1.0.0",
        "triggerOperator": "GreaterThan",
        "triggerThreshold": 1
      },
      "type": "Microsoft.OperationalInsights/workspaces/providers/alertRules"
    }
  ]
}