AWSCloudTrail - S3 Object Exfiltration from Anonymous User

AWSCloudTrail
| where ((UserIdentityAccountId =~ @'ANONYMOUS_PRINCIPAL' or UserIdentityPrincipalid == "Anonymous") and EventName == 'GetObject')
| extend
   BucketName = parse_json(RequestParameters).bucketName,
   ObjectKey = parse_json(RequestParameters).key
| extend UserName = substring(UserIdentityPrincipalid, indexof_regex(UserIdentityPrincipalid, ":") + 1)
| extend Name = split(UserName,'@')[0],UpnSuffix = split(UserName,'@')[1]

name: AWSCloudTrail - S3 Object Exfiltration from Anonymous User
triggerOperator: gt
query: |
  AWSCloudTrail
  | where ((UserIdentityAccountId =~ @'ANONYMOUS_PRINCIPAL' or UserIdentityPrincipalid == "Anonymous") and EventName == 'GetObject')
  | extend
     BucketName = parse_json(RequestParameters).bucketName,
     ObjectKey = parse_json(RequestParameters).key
  | extend UserName = substring(UserIdentityPrincipalid, indexof_regex(UserIdentityPrincipalid, ":") + 1)
  | extend Name = split(UserName,'@')[0],UpnSuffix = split(UserName,'@')[1]
queryFrequency: 5m
description: |
  Detects S3 GetObject activity performed by anonymous principals, which can indicate unauthorized object access
  and potential data exfiltration from public or misconfigured buckets.
id: 15d3bf4e-8708-41c8-a836-8b0aa5be730e
triggerThreshold: 0
queryPeriod: 5m
version: 1.0.1
kind: Scheduled
customDetails:
  BucketName: BucketName
  ObjectKey: ObjectKey
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_S3ObjectExfiltrationByAnonymousUser.yaml
alertDetailsOverride:
  alertDescriptionFormat: Detected anonymous GetObject activity for bucket {{BucketName}} and object {{ObjectKey}} from {{SourceIpAddress}}.
  alertDisplayNameFormat: AWS S3 object access by anonymous principal in bucket {{BucketName}}
relevantTechniques:
- T1530
tactics:
- Collection
entityMappings:
- fieldMappings:
  - identifier: Name
    columnName: Name
  - identifier: UPNSuffix
    columnName: UpnSuffix
  entityType: Account
- fieldMappings:
  - identifier: Address
    columnName: SourceIpAddress
  entityType: IP

{
  "$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/15d3bf4e-8708-41c8-a836-8b0aa5be730e')]",
      "kind": "Scheduled",
      "name": "[concat(parameters('workspace'),'/Microsoft.SecurityInsights/15d3bf4e-8708-41c8-a836-8b0aa5be730e')]",
      "properties": {
        "alertDetailsOverride": {
          "alertDescriptionFormat": "Detected anonymous GetObject activity for bucket {{BucketName}} and object {{ObjectKey}} from {{SourceIpAddress}}.",
          "alertDisplayNameFormat": "AWS S3 object access by anonymous principal in bucket {{BucketName}}"
        },
        "alertRuleTemplateName": "15d3bf4e-8708-41c8-a836-8b0aa5be730e",
        "customDetails": {
          "BucketName": "BucketName",
          "ObjectKey": "ObjectKey"
        },
        "description": "Detects S3 GetObject activity performed by anonymous principals, which can indicate unauthorized object access\nand potential data exfiltration from public or misconfigured buckets.\n",
        "displayName": "AWSCloudTrail - S3 Object Exfiltration from Anonymous User",
        "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_S3ObjectExfiltrationByAnonymousUser.yaml",
        "query": "AWSCloudTrail\n| where ((UserIdentityAccountId =~ @'ANONYMOUS_PRINCIPAL' or UserIdentityPrincipalid == \"Anonymous\") and EventName == 'GetObject')\n| extend\n   BucketName = parse_json(RequestParameters).bucketName,\n   ObjectKey = parse_json(RequestParameters).key\n| extend UserName = substring(UserIdentityPrincipalid, indexof_regex(UserIdentityPrincipalid, \":\") + 1)\n| extend Name = split(UserName,'@')[0],UpnSuffix = split(UserName,'@')[1]\n",
        "queryFrequency": "PT5M",
        "queryPeriod": "PT5M",
        "severity": "Medium",
        "status": "Available",
        "subTechniques": [],
        "suppressionDuration": "PT1H",
        "suppressionEnabled": false,
        "tactics": [
          "Collection"
        ],
        "techniques": [
          "T1530"
        ],
        "templateVersion": "1.0.1",
        "triggerOperator": "GreaterThan",
        "triggerThreshold": 0
      },
      "type": "Microsoft.OperationalInsights/workspaces/providers/alertRules"
    }
  ]
}