AWSCloudTrail - S3 object publicly exposed

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Id	09f2a28b-3286-4268-9e2f-33805f104e5d
Rulename	AWSCloudTrail - S3 object publicly exposed
Description	Detects S3 object ACL changes that expose objects to public or broadly authenticated users. This can result in unintended data disclosure from object-level permissions.
Severity	Medium
Tactics	Exfiltration
Techniques	T1537
Required data connectors	AWS
Kind	Scheduled
Query frequency	1h
Query period	1h
Trigger threshold	0
Trigger operator	gt
Source Uri	https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/Amazon Web Services/Analytic Rules/AWS_S3ObjectPubliclyExposed.yaml
Version	1.0.2
Arm template	09f2a28b-3286-4268-9e2f-33805f104e5d.json

KQL

AWSCloudTrail
  | where EventName == "PutObjectAcl" and isempty(ErrorCode) and isempty(ErrorMessage)
  | extend Grant = parse_json(tostring((parse_json(RequestParameters).AccessControlPolicy))).AccessControlList.Grant
  | mvexpand Grant
  | extend cannedacl = parse_json(tostring((parse_json(RequestParameters))))
  | extend URI = parse_json(Grant).Grantee.URI, type = parse_json(Grant).Grantee.["xsi:type"], xamzacl = parse_json(cannedacl).["x-amz-acl"]
  | where (type == "Group" and (URI endswith "AllUsers" or URI endswith "AuthenticatedUsers"))
    or xamzacl in ("authenticated-read","public-read","public-read-write")
  | extend UserIdentityArn = iif(isempty(UserIdentityArn), tostring(parse_json(Resources)[0].ARN), UserIdentityArn)
  | extend UserName = tostring(split(UserIdentityArn, '/')[-1])
  | extend AccountName = case( UserIdentityPrincipalid == "Anonymous", "Anonymous", isempty(UserIdentityUserName), UserName, UserIdentityUserName)
  | extend AccountName = iif(AccountName contains "@", tostring(split(AccountName, '@', 0)[0]), AccountName),
    AccountUPNSuffix = iif(AccountName contains "@", tostring(split(AccountName, '@', 1)[0]), "")

YAML

status: Available
queryFrequency: 1h
queryPeriod: 1h
triggerOperator: gt
query: |
  AWSCloudTrail
    | where EventName == "PutObjectAcl" and isempty(ErrorCode) and isempty(ErrorMessage)
    | extend Grant = parse_json(tostring((parse_json(RequestParameters).AccessControlPolicy))).AccessControlList.Grant
    | mvexpand Grant
    | extend cannedacl = parse_json(tostring((parse_json(RequestParameters))))
    | extend URI = parse_json(Grant).Grantee.URI, type = parse_json(Grant).Grantee.["xsi:type"], xamzacl = parse_json(cannedacl).["x-amz-acl"]
    | where (type == "Group" and (URI endswith "AllUsers" or URI endswith "AuthenticatedUsers"))
      or xamzacl in ("authenticated-read","public-read","public-read-write")
    | extend UserIdentityArn = iif(isempty(UserIdentityArn), tostring(parse_json(Resources)[0].ARN), UserIdentityArn)
    | extend UserName = tostring(split(UserIdentityArn, '/')[-1])
    | extend AccountName = case( UserIdentityPrincipalid == "Anonymous", "Anonymous", isempty(UserIdentityUserName), UserName, UserIdentityUserName)
    | extend AccountName = iif(AccountName contains "@", tostring(split(AccountName, '@', 0)[0]), AccountName),
      AccountUPNSuffix = iif(AccountName contains "@", tostring(split(AccountName, '@', 1)[0]), "")  
OriginalUri: https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/Amazon Web Services/Analytic Rules/AWS_S3ObjectPubliclyExposed.yaml
tactics:
- Exfiltration
triggerThreshold: 0
entityMappings:
- entityType: Account
  fieldMappings:
  - identifier: Name
    columnName: AccountName
  - identifier: UPNSuffix
    columnName: AccountUPNSuffix
  - identifier: CloudAppAccountId
    columnName: RecipientAccountId
- entityType: IP
  fieldMappings:
  - identifier: Address
    columnName: SourceIpAddress
requiredDataConnectors:
- connectorId: AWS
  dataTypes:
  - AWSCloudTrail
alertDetailsOverride:
  alertDescriptionFormat: Detected {{EventName}} event from {{SourceIpAddress}} applying public object ACL settings in account {{RecipientAccountId}}.
  alertDisplayNameFormat: AWS S3 object public ACL exposure by {{AccountName}}
relevantTechniques:
- T1537
customDetails:
  xamzacl: xamzacl
  EventName: EventName
  URI: URI
  RecipientAccountId: RecipientAccountId
description: |
  Detects S3 object ACL changes that expose objects to public or broadly authenticated users.
  This can result in unintended data disclosure from object-level permissions.  
name: AWSCloudTrail - S3 object publicly exposed
version: 1.0.2
kind: Scheduled
id: 09f2a28b-3286-4268-9e2f-33805f104e5d
severity: Medium

ARM