Windows host username encoded in base64 web request

let accountLookback = 3d;
let requestLookback = 3d;
let extraction_regex = @"(?:\?|&)[a-zA-Z0-9\%]*=([a-zA-Z0-9\/\+\=]*)";
// Collect account names and base64 encode them
DeviceEvents
| where TimeGenerated > ago(accountLookback)
| summarize make_set(DeviceId), make_set(DeviceName) by InitiatingProcessAccountName
| where isnotempty(InitiatingProcessAccountName)
| extend base64_user = base64_encode_tostring(InitiatingProcessAccountName)
| join (
    // Collect requests and extract base64 parameters
    CommonSecurityLog
    | where TimeGenerated > ago(requestLookback)
    | where isnotempty(RequestURL)
    // Summarize early on the RequestURL
    | summarize FirstRequest=min(TimeGenerated), LastRequest=max(TimeGenerated), NumberOfRequests=count() by RequestURL
    | extend base64_candidate = extract_all(extraction_regex, RequestURL)
    | mv-expand base64_candidate  to typeof(string)
) on $left.base64_user == $right.base64_candidate
| project FirstRequest, LastRequest, NumberOfRequests, RequestURL, DeviceIds=set_DeviceId, DeviceNames=set_DeviceName, UserName=InitiatingProcessAccountName

relevantTechniques:
- T1041
- T1071.001
queryPeriod: 1d
tactics:
- Exfiltration
- CommandAndControl
requiredDataConnectors:
- dataTypes:
  - CommonSecurityLog
  connectorId: Zscaler
- dataTypes:
  - CommonSecurityLog
  connectorId: Fortinet
- dataTypes:
  - CommonSecurityLog
  connectorId: CheckPoint
- dataTypes:
  - CommonSecurityLog
  connectorId: PaloAltoNetworks
- dataTypes:
  - DeviceNetworkEvents
  connectorId: MicrosoftThreatProtection
triggerThreshold: 0
entityMappings:
- fieldMappings:
  - identifier: HostName
    columnName: DeviceNames
  entityType: Host
- fieldMappings:
  - identifier: Url
    columnName: RequestURL
  entityType: URL
- fieldMappings:
  - identifier: Name
    columnName: UserName
  entityType: Account
name: Windows host username encoded in base64 web request
tags:
- POLONIUM
query: |
  let accountLookback = 3d;
  let requestLookback = 3d;
  let extraction_regex = @"(?:\?|&)[a-zA-Z0-9\%]*=([a-zA-Z0-9\/\+\=]*)";
  // Collect account names and base64 encode them
  DeviceEvents
  | where TimeGenerated > ago(accountLookback)
  | summarize make_set(DeviceId), make_set(DeviceName) by InitiatingProcessAccountName
  | where isnotempty(InitiatingProcessAccountName)
  | extend base64_user = base64_encode_tostring(InitiatingProcessAccountName)
  | join (
      // Collect requests and extract base64 parameters
      CommonSecurityLog
      | where TimeGenerated > ago(requestLookback)
      | where isnotempty(RequestURL)
      // Summarize early on the RequestURL
      | summarize FirstRequest=min(TimeGenerated), LastRequest=max(TimeGenerated), NumberOfRequests=count() by RequestURL
      | extend base64_candidate = extract_all(extraction_regex, RequestURL)
      | mv-expand base64_candidate  to typeof(string)
  ) on $left.base64_user == $right.base64_candidate
  | project FirstRequest, LastRequest, NumberOfRequests, RequestURL, DeviceIds=set_DeviceId, DeviceNames=set_DeviceName, UserName=InitiatingProcessAccountName  
queryFrequency: 1d
id: 6e715730-82c0-496c-983b-7a20c4590bd9
severity: Medium
description: |
  'This detection will identify network requests in HTTP proxy data that contains Base64 encoded usernames from machines in the DeviceEvents table.
  This technique was seen usee by POLONIUM in their RunningRAT tool.'  
metadata:
  source:
    kind: Community
  categories:
    domains:
    - Security - Others
  support:
    tier: Community
  author:
    name: Thomas McElroy
version: 1.0.1
OriginalUri: https://github.com/Azure/Azure-Sentinel/blob/master/Detections/MultipleDataSources/B64UserInWebURIFromMDE.yaml
kind: Scheduled
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": "2023-02-01-preview",
      "id": "[concat(resourceId('Microsoft.OperationalInsights/workspaces/providers', parameters('workspace'), 'Microsoft.SecurityInsights'),'/alertRules/6e715730-82c0-496c-983b-7a20c4590bd9')]",
      "kind": "Scheduled",
      "name": "[concat(parameters('workspace'),'/Microsoft.SecurityInsights/6e715730-82c0-496c-983b-7a20c4590bd9')]",
      "properties": {
        "alertRuleTemplateName": "6e715730-82c0-496c-983b-7a20c4590bd9",
        "customDetails": null,
        "description": "'This detection will identify network requests in HTTP proxy data that contains Base64 encoded usernames from machines in the DeviceEvents table.\nThis technique was seen usee by POLONIUM in their RunningRAT tool.'\n",
        "displayName": "Windows host username encoded in base64 web request",
        "enabled": true,
        "entityMappings": [
          {
            "entityType": "Host",
            "fieldMappings": [
              {
                "columnName": "DeviceNames",
                "identifier": "HostName"
              }
            ]
          },
          {
            "entityType": "URL",
            "fieldMappings": [
              {
                "columnName": "RequestURL",
                "identifier": "Url"
              }
            ]
          },
          {
            "entityType": "Account",
            "fieldMappings": [
              {
                "columnName": "UserName",
                "identifier": "Name"
              }
            ]
          }
        ],
        "OriginalUri": "https://github.com/Azure/Azure-Sentinel/blob/master/Detections/MultipleDataSources/B64UserInWebURIFromMDE.yaml",
        "query": "let accountLookback = 3d;\nlet requestLookback = 3d;\nlet extraction_regex = @\"(?:\\?|&)[a-zA-Z0-9\\%]*=([a-zA-Z0-9\\/\\+\\=]*)\";\n// Collect account names and base64 encode them\nDeviceEvents\n| where TimeGenerated > ago(accountLookback)\n| summarize make_set(DeviceId), make_set(DeviceName) by InitiatingProcessAccountName\n| where isnotempty(InitiatingProcessAccountName)\n| extend base64_user = base64_encode_tostring(InitiatingProcessAccountName)\n| join (\n    // Collect requests and extract base64 parameters\n    CommonSecurityLog\n    | where TimeGenerated > ago(requestLookback)\n    | where isnotempty(RequestURL)\n    // Summarize early on the RequestURL\n    | summarize FirstRequest=min(TimeGenerated), LastRequest=max(TimeGenerated), NumberOfRequests=count() by RequestURL\n    | extend base64_candidate = extract_all(extraction_regex, RequestURL)\n    | mv-expand base64_candidate  to typeof(string)\n) on $left.base64_user == $right.base64_candidate\n| project FirstRequest, LastRequest, NumberOfRequests, RequestURL, DeviceIds=set_DeviceId, DeviceNames=set_DeviceName, UserName=InitiatingProcessAccountName\n",
        "queryFrequency": "P1D",
        "queryPeriod": "P1D",
        "severity": "Medium",
        "suppressionDuration": "PT1H",
        "suppressionEnabled": false,
        "tactics": [
          "CommandAndControl",
          "Exfiltration"
        ],
        "tags": [
          "POLONIUM"
        ],
        "techniques": [
          "T1041",
          "T1071"
        ],
        "templateVersion": "1.0.1",
        "triggerOperator": "GreaterThan",
        "triggerThreshold": 0
      },
      "type": "Microsoft.OperationalInsights/workspaces/providers/alertRules"
    }
  ]
}