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

metadata:
  categories:
    domains:
    - Security - Others
  support:
    tier: Community
  source:
    kind: Community
  author:
    name: Thomas McElroy
tags:
- POLONIUM
OriginalUri: https://github.com/Azure/Azure-Sentinel/blob/master/Detections/MultipleDataSources/B64UserInWebURIFromMDE.yaml
severity: Medium
version: 1.0.1
queryPeriod: 1d
kind: Scheduled
relevantTechniques:
- T1041
- T1071.001
name: Windows host username encoded in base64 web request
entityMappings:
- entityType: Host
  fieldMappings:
  - columnName: DeviceNames
    identifier: HostName
- entityType: URL
  fieldMappings:
  - columnName: RequestURL
    identifier: Url
- entityType: Account
  fieldMappings:
  - columnName: UserName
    identifier: Name
requiredDataConnectors:
- connectorId: Zscaler
  dataTypes:
  - CommonSecurityLog
- connectorId: Fortinet
  dataTypes:
  - CommonSecurityLog
- connectorId: CheckPoint
  dataTypes:
  - CommonSecurityLog
- connectorId: PaloAltoNetworks
  dataTypes:
  - CommonSecurityLog
- connectorId: MicrosoftThreatProtection
  dataTypes:
  - DeviceNetworkEvents
id: 6e715730-82c0-496c-983b-7a20c4590bd9
triggerThreshold: 0
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.'
triggerOperator: gt
queryFrequency: 1d
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
tactics:
- Exfiltration
- CommandAndControl

{
  "$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"
    }
  ]
}