AWSCloudTrail - EC2 Startup Shell Script Changed | Microsoft Sentinel Analytic Rules

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Id	f8577e4d-8481-437b-a94e-06f615985668
Rulename	AWSCloudTrail - EC2 Startup Shell Script Changed
Description	Identifies changes to the EC2 startup script. The shell script will be executed as root/SYSTEM every time the specific instances are booted up. ref : https://github.com/RhinoSecurityLabs/pacu/blob/master/pacu/modules/ec2__startup_shell_script/main.py
Severity	Medium
Tactics	Execution
Techniques	T1059
Required data connectors	AWS
Kind	Scheduled
Query frequency	15m
Query period	15m
Trigger threshold	0
Trigger operator	gt
Source Uri	https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/Amazon%20Web%20Services/Analytic%20Rules/AWS_EC2StartupShellScriptChanged.yaml
Version	1.0.1
Arm template	f8577e4d-8481-437b-a94e-06f615985668.json

KQL

AWSCloudTrail
| where EventName in~ ("ModifyInstanceAttribute", "CreateLaunchTemplate")
| extend RequestParametersJson = parse_json(RequestParameters)
| where tostring(RequestParametersJson.userData) != ""
| extend userData_ = tostring(RequestParametersJson.userData)
| extend instanceId_ = tostring(RequestParametersJson.instanceId)
| project-away SourceSystem, Category, Type, TenantId, EventVersion, SessionIssuerAccountId
| extend UserName = substring(UserIdentityPrincipalid, indexof_regex(UserIdentityPrincipalid, ":") + 1)
| extend Name = split(UserName,'@')[0],UpnSuffix = split(UserName,'@')[1]
| project TimeGenerated, EventName, UserName, Name, UpnSuffix, instanceId_, AWSRegion, SourceIpAddress, EventSource, UserIdentityArn, EventTypeName

YAML

name: AWSCloudTrail - EC2 Startup Shell Script Changed
triggerOperator: gt
query: |
  AWSCloudTrail
  | where EventName in~ ("ModifyInstanceAttribute", "CreateLaunchTemplate")
  | extend RequestParametersJson = parse_json(RequestParameters)
  | where tostring(RequestParametersJson.userData) != ""
  | extend userData_ = tostring(RequestParametersJson.userData)
  | extend instanceId_ = tostring(RequestParametersJson.instanceId)
  | project-away SourceSystem, Category, Type, TenantId, EventVersion, SessionIssuerAccountId
  | extend UserName = substring(UserIdentityPrincipalid, indexof_regex(UserIdentityPrincipalid, ":") + 1)
  | extend Name = split(UserName,'@')[0],UpnSuffix = split(UserName,'@')[1]
  | project TimeGenerated, EventName, UserName, Name, UpnSuffix, instanceId_, AWSRegion, SourceIpAddress, EventSource, UserIdentityArn, EventTypeName
queryFrequency: 15m
description: |
  Identifies changes to the EC2 startup script. The shell script will be executed as root/SYSTEM every time the specific instances are booted up. ref : https://github.com/RhinoSecurityLabs/pacu/blob/master/pacu/modules/ec2__startup_shell_script/main.py
id: f8577e4d-8481-437b-a94e-06f615985668
triggerThreshold: 0
queryPeriod: 15m
version: 1.0.1
kind: Scheduled
customDetails:
  InstanceId: instanceId_
  EventName: EventName
  EventType: EventTypeName
  AWSRegion: AWSRegion
  EventSource: EventSource
status: Available
severity: Medium
requiredDataConnectors:
- connectorId: AWS
  dataTypes:
  - AWSCloudTrail
OriginalUri: https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/Amazon%20Web%20Services/Analytic%20Rules/AWS_EC2StartupShellScriptChanged.yaml
alertDetailsOverride:
  alertDescriptionFormat: EC2 startup script changed on {{instanceId_}} by {{UserName}} in {{AWSRegion}}.
  alertDisplayNameFormat: EC2 startup script changed on {{instanceId_}} by {{UserName}}
relevantTechniques:
- T1059
tactics:
- Execution
entityMappings:
- fieldMappings:
  - identifier: Name
    columnName: Name
  - identifier: UPNSuffix
    columnName: UpnSuffix
  entityType: Account
- fieldMappings:
  - identifier: Address
    columnName: SourceIpAddress
  entityType: IP

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/f8577e4d-8481-437b-a94e-06f615985668')]",
      "kind": "Scheduled",
      "name": "[concat(parameters('workspace'),'/Microsoft.SecurityInsights/f8577e4d-8481-437b-a94e-06f615985668')]",
      "properties": {
        "alertDetailsOverride": {
          "alertDescriptionFormat": "EC2 startup script changed on {{instanceId_}} by {{UserName}} in {{AWSRegion}}.",
          "alertDisplayNameFormat": "EC2 startup script changed on {{instanceId_}} by {{UserName}}"
        },
        "alertRuleTemplateName": "f8577e4d-8481-437b-a94e-06f615985668",
        "customDetails": {
          "AWSRegion": "AWSRegion",
          "EventName": "EventName",
          "EventSource": "EventSource",
          "EventType": "EventTypeName",
          "InstanceId": "instanceId_"
        },
        "description": "Identifies changes to the EC2 startup script. The shell script will be executed as root/SYSTEM every time the specific instances are booted up. ref : https://github.com/RhinoSecurityLabs/pacu/blob/master/pacu/modules/ec2__startup_shell_script/main.py\n",
        "displayName": "AWSCloudTrail - EC2 Startup Shell Script Changed",
        "enabled": true,
        "entityMappings": [
          {
            "entityType": "Account",
            "fieldMappings": [
              {
                "columnName": "Name",
                "identifier": "Name"
              },
              {
                "columnName": "UpnSuffix",
                "identifier": "UPNSuffix"
              }
            ]
          },
          {
            "entityType": "IP",
            "fieldMappings": [
              {
                "columnName": "SourceIpAddress",
                "identifier": "Address"
              }
            ]
          }
        ],
        "OriginalUri": "https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/Amazon%20Web%20Services/Analytic%20Rules/AWS_EC2StartupShellScriptChanged.yaml",
        "query": "AWSCloudTrail\n| where EventName in~ (\"ModifyInstanceAttribute\", \"CreateLaunchTemplate\")\n| extend RequestParametersJson = parse_json(RequestParameters)\n| where tostring(RequestParametersJson.userData) != \"\"\n| extend userData_ = tostring(RequestParametersJson.userData)\n| extend instanceId_ = tostring(RequestParametersJson.instanceId)\n| project-away SourceSystem, Category, Type, TenantId, EventVersion, SessionIssuerAccountId\n| extend UserName = substring(UserIdentityPrincipalid, indexof_regex(UserIdentityPrincipalid, \":\") + 1)\n| extend Name = split(UserName,'@')[0],UpnSuffix = split(UserName,'@')[1]\n| project TimeGenerated, EventName, UserName, Name, UpnSuffix, instanceId_, AWSRegion, SourceIpAddress, EventSource, UserIdentityArn, EventTypeName\n",
        "queryFrequency": "PT15M",
        "queryPeriod": "PT15M",
        "severity": "Medium",
        "status": "Available",
        "subTechniques": [],
        "suppressionDuration": "PT1H",
        "suppressionEnabled": false,
        "tactics": [
          "Execution"
        ],
        "techniques": [
          "T1059"
        ],
        "templateVersion": "1.0.1",
        "triggerOperator": "GreaterThan",
        "triggerThreshold": 0
      },
      "type": "Microsoft.OperationalInsights/workspaces/providers/alertRules"
    }
  ]
}