AWSCloudTrail - S3 bucket exposed via ACL

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Id	6b9b4ee6-f4c1-4b86-8c8c-beb0bb59ae44
Rulename	AWSCloudTrail - S3 bucket exposed via ACL
Description	Detects S3 bucket ACL changes that grant public or broadly authenticated access. Overly permissive ACL assignments can expose bucket contents to unauthorized users.
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_S3BucketExposedviaACL.yaml
Version	1.0.2
Arm template	6b9b4ee6-f4c1-4b86-8c8c-beb0bb59ae44.json

KQL

AWSCloudTrail
| where EventName == "PutBucketAcl" and isempty(ErrorCode) and isempty(ErrorMessage)
| 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]), "")
| 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")

YAML

status: Available
queryFrequency: 1h
queryPeriod: 1h
triggerOperator: gt
query: |
  AWSCloudTrail
  | where EventName == "PutBucketAcl" and isempty(ErrorCode) and isempty(ErrorMessage)
  | 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]), "")
  | 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")  
OriginalUri: https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/Amazon Web Services/Analytic Rules/AWS_S3BucketExposedviaACL.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}} from {{SourceIpAddress}} applying public or broad ACL on S3 bucket in account {{RecipientAccountId}}.
  alertDisplayNameFormat: AWS S3 bucket ACL exposure change by {{AccountName}}
relevantTechniques:
- T1537
customDetails:
  xamzacl: xamzacl
  EventName: EventName
  URI: URI
  RecipientAccountId: RecipientAccountId
description: |
  Detects S3 bucket ACL changes that grant public or broadly authenticated access. Overly permissive ACL
  assignments can expose bucket contents to unauthorized users.  
name: AWSCloudTrail - S3 bucket exposed via ACL
version: 1.0.2
kind: Scheduled
id: 6b9b4ee6-f4c1-4b86-8c8c-beb0bb59ae44
severity: Medium

ARM