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
name: Windows host username encoded in base64 web request
requiredDataConnectors:
- dataTypes:
  - CommonSecurityLog
  connectorId: Zscaler
- dataTypes:
  - CommonSecurityLog
  connectorId: Fortinet
- dataTypes:
  - CommonSecurityLog
  connectorId: CheckPoint
- dataTypes:
  - CommonSecurityLog
  connectorId: PaloAltoNetworks
- dataTypes:
  - DeviceNetworkEvents
  connectorId: MicrosoftThreatProtection
entityMappings:
- fieldMappings:
  - identifier: HostName
    columnName: DeviceNames
  entityType: Host
- fieldMappings:
  - identifier: Url
    columnName: RequestURL
  entityType: URL
- fieldMappings:
  - identifier: Name
    columnName: UserName
  entityType: Account
triggerThreshold: 0
id: 6e715730-82c0-496c-983b-7a20c4590bd9
tactics:
- Exfiltration
- CommandAndControl
version: 1.0.1
OriginalUri: https://github.com/Azure/Azure-Sentinel/blob/master/Detections/MultipleDataSources/B64UserInWebURIFromMDE.yaml
queryPeriod: 1d
kind: Scheduled
tags:
- POLONIUM
metadata:
  categories:
    domains:
    - Security - Others
  author:
    name: Thomas McElroy
  support:
    tier: Community
  source:
    kind: Community
queryFrequency: 1d
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.'  
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  
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/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",
        "subTechniques": [
          "T1071.001"
        ],
        "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"
    }
  ]
}