Anomalous User Agent connection attempt

let short_uaLength = 5;
let long_uaLength = 1000;
let c_threshold = 100;
W3CIISLog
// Exclude local IPs as these create noise
| where cIP !startswith "192.168." and cIP != "::1"
| where isnotempty(csUserAgent) and csUserAgent !in~ ("-", "MSRPC") and (string_size(csUserAgent) <= short_uaLength or string_size(csUserAgent) >= long_uaLength)
| extend csUserAgent_size = string_size(csUserAgent)
| summarize StartTimeUtc = min(TimeGenerated), EndTimeUtc = max(TimeGenerated), ConnectionCount = count() by Computer, sSiteName, sPort, csUserAgent, csUserAgent_size, csUserName , csMethod, csUriStem, sIP, cIP, scStatus, scSubStatus, scWin32Status
| where ConnectionCount < c_threshold
| extend timestamp = StartTimeUtc, AccountCustomEntity = csUserName, HostCustomEntity = Computer, IPCustomEntity = cIP

name: Anomalous User Agent connection attempt
query: |
  let short_uaLength = 5;
  let long_uaLength = 1000;
  let c_threshold = 100;
  W3CIISLog
  // Exclude local IPs as these create noise
  | where cIP !startswith "192.168." and cIP != "::1"
  | where isnotempty(csUserAgent) and csUserAgent !in~ ("-", "MSRPC") and (string_size(csUserAgent) <= short_uaLength or string_size(csUserAgent) >= long_uaLength)
  | extend csUserAgent_size = string_size(csUserAgent)
  | summarize StartTimeUtc = min(TimeGenerated), EndTimeUtc = max(TimeGenerated), ConnectionCount = count() by Computer, sSiteName, sPort, csUserAgent, csUserAgent_size, csUserName , csMethod, csUriStem, sIP, cIP, scStatus, scSubStatus, scWin32Status
  | where ConnectionCount < c_threshold
  | extend timestamp = StartTimeUtc, AccountCustomEntity = csUserName, HostCustomEntity = Computer, IPCustomEntity = cIP  
OriginalUri: https://github.com/Azure/Azure-Sentinel/blob/master/Detections/W3CIISLog/AnomomlousUserAgentConnection.yaml
queryFrequency: 1d
triggerThreshold: 0
requiredDataConnectors:
- dataTypes:
  - W3CIISLog
  connectorId: AzureMonitor(IIS)
version: 1.0.2
queryPeriod: 1d
id: f845881e-2500-44dc-8ed7-b372af3e1e25
triggerOperator: gt
entityMappings:
- fieldMappings:
  - identifier: FullName
    columnName: AccountCustomEntity
  entityType: Account
- fieldMappings:
  - identifier: FullName
    columnName: HostCustomEntity
  entityType: Host
- fieldMappings:
  - identifier: Address
    columnName: IPCustomEntity
  entityType: IP
metadata:
  source:
    kind: Community
  author:
    name: Shain
  categories:
    domains:
    - Security - Threat Protection
  support:
    tier: Community
relevantTechniques:
- T1190
severity: Low
description: |
    'Identifies connection attempts (success or fail) from clients with very short or very long User Agent strings and with less than 100 connection attempts.'
kind: Scheduled
tactics:
- InitialAccess

{
  "$schema": "https://schema.management.azure.com/schemas/2019-04-01/deploymentTemplate.json#",
  "contentVersion": "1.0.0.0",
  "parameters": {
    "workspace": {
      "type": "String"
    }
  },
  "resources": [
    {
      "id": "[concat(resourceId('Microsoft.OperationalInsights/workspaces/providers', parameters('workspace'), 'Microsoft.SecurityInsights'),'/alertRules/f845881e-2500-44dc-8ed7-b372af3e1e25')]",
      "name": "[concat(parameters('workspace'),'/Microsoft.SecurityInsights/f845881e-2500-44dc-8ed7-b372af3e1e25')]",
      "type": "Microsoft.OperationalInsights/workspaces/providers/alertRules",
      "kind": "Scheduled",
      "apiVersion": "2022-11-01",
      "properties": {
        "displayName": "Anomalous User Agent connection attempt",
        "description": "'Identifies connection attempts (success or fail) from clients with very short or very long User Agent strings and with less than 100 connection attempts.'\n",
        "severity": "Low",
        "enabled": true,
        "query": "let short_uaLength = 5;\nlet long_uaLength = 1000;\nlet c_threshold = 100;\nW3CIISLog\n// Exclude local IPs as these create noise\n| where cIP !startswith \"192.168.\" and cIP != \"::1\"\n| where isnotempty(csUserAgent) and csUserAgent !in~ (\"-\", \"MSRPC\") and (string_size(csUserAgent) <= short_uaLength or string_size(csUserAgent) >= long_uaLength)\n| extend csUserAgent_size = string_size(csUserAgent)\n| summarize StartTimeUtc = min(TimeGenerated), EndTimeUtc = max(TimeGenerated), ConnectionCount = count() by Computer, sSiteName, sPort, csUserAgent, csUserAgent_size, csUserName , csMethod, csUriStem, sIP, cIP, scStatus, scSubStatus, scWin32Status\n| where ConnectionCount < c_threshold\n| extend timestamp = StartTimeUtc, AccountCustomEntity = csUserName, HostCustomEntity = Computer, IPCustomEntity = cIP\n",
        "queryFrequency": "P1D",
        "queryPeriod": "P1D",
        "triggerOperator": "GreaterThan",
        "triggerThreshold": 0,
        "suppressionDuration": "PT1H",
        "suppressionEnabled": false,
        "tactics": [
          "InitialAccess"
        ],
        "techniques": [
          "T1190"
        ],
        "alertRuleTemplateName": "f845881e-2500-44dc-8ed7-b372af3e1e25",
        "customDetails": null,
        "entityMappings": [
          {
            "fieldMappings": [
              {
                "identifier": "FullName",
                "columnName": "AccountCustomEntity"
              }
            ],
            "entityType": "Account"
          },
          {
            "fieldMappings": [
              {
                "identifier": "FullName",
                "columnName": "HostCustomEntity"
              }
            ],
            "entityType": "Host"
          },
          {
            "fieldMappings": [
              {
                "identifier": "Address",
                "columnName": "IPCustomEntity"
              }
            ],
            "entityType": "IP"
          }
        ],
        "templateVersion": "1.0.2",
        "OriginalUri": "https://github.com/Azure/Azure-Sentinel/blob/master/Detections/W3CIISLog/AnomomlousUserAgentConnection.yaml"
      }
    }
  ]
}