AWSCloudTrail - S3 bucket access point publicly exposed

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Id	b7a44e0d-ae4c-4fb2-be1b-aa0e45f2327b
Rulename	AWSCloudTrail - S3 bucket access point publicly exposed
Description	Detects S3 access point policy changes that allow public principals. Public exposure through access point configuration can lead to unauthorized data access and potential information disclosure.
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_S3BucketAccessPointExposed.yaml
Version	1.0.2
Arm template	b7a44e0d-ae4c-4fb2-be1b-aa0e45f2327b.json

KQL

AWSCloudTrail
| where EventName == "PutAccessPointPolicy" and isempty(ErrorCode) and isempty(ErrorMessage)
| extend Statement = parse_json(tostring((parse_json(RequestParameters).PutAccessPointPolicyRequest.Policy))).Statement
| mvexpand Statement
| extend Action = parse_json(Statement).Action , Effect = tostring(parse_json(Statement).Effect), Resource = tostring(parse_json(Statement).Resource), Condition = tostring(parse_json(Statement).Condition), Principal_aws = tostring(parse_json(Statement).Principal.AWS), Principal = tostring(parse_json(Statement).Principal)
| extend Action = tostring(Action)
| where Effect =~ "Allow" and (Principal_aws == "*" or Principal == "*") and isempty(Condition)
| 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]), "")
| distinct TimeGenerated, EventName, SourceIpAddress, RecipientAccountId, AccountName, AccountUPNSuffix, UserIdentityArn, UserIdentityUserName

YAML

version: 1.0.2
id: b7a44e0d-ae4c-4fb2-be1b-aa0e45f2327b
relevantTechniques:
- T1537
requiredDataConnectors:
- connectorId: AWS
  dataTypes:
  - AWSCloudTrail
alertDetailsOverride:
  alertDescriptionFormat: Detected {{EventName}} from {{SourceIpAddress}} creating public S3 access point exposure in account {{RecipientAccountId}}.
  alertDisplayNameFormat: AWS S3 access point publicly exposed by {{AccountName}}
triggerOperator: gt
entityMappings:
- fieldMappings:
  - columnName: AccountName
    identifier: Name
  - columnName: AccountUPNSuffix
    identifier: UPNSuffix
  - columnName: RecipientAccountId
    identifier: CloudAppAccountId
  entityType: Account
- fieldMappings:
  - columnName: SourceIpAddress
    identifier: Address
  entityType: IP
name: AWSCloudTrail - S3 bucket access point publicly exposed
queryFrequency: 1h
triggerThreshold: 0
customDetails:
  UserIdentityArn: UserIdentityArn
  RecipientAccountId: RecipientAccountId
  EventName: EventName
description: |
  Detects S3 access point policy changes that allow public principals. Public exposure through access point
  configuration can lead to unauthorized data access and potential information disclosure.  
status: Available
OriginalUri: https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/Amazon Web Services/Analytic Rules/AWS_S3BucketAccessPointExposed.yaml
queryPeriod: 1h
severity: Medium
kind: Scheduled
tactics:
- Exfiltration
query: |
  AWSCloudTrail
  | where EventName == "PutAccessPointPolicy" and isempty(ErrorCode) and isempty(ErrorMessage)
  | extend Statement = parse_json(tostring((parse_json(RequestParameters).PutAccessPointPolicyRequest.Policy))).Statement
  | mvexpand Statement
  | extend Action = parse_json(Statement).Action , Effect = tostring(parse_json(Statement).Effect), Resource = tostring(parse_json(Statement).Resource), Condition = tostring(parse_json(Statement).Condition), Principal_aws = tostring(parse_json(Statement).Principal.AWS), Principal = tostring(parse_json(Statement).Principal)
  | extend Action = tostring(Action)
  | where Effect =~ "Allow" and (Principal_aws == "*" or Principal == "*") and isempty(Condition)
  | 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]), "")
  | distinct TimeGenerated, EventName, SourceIpAddress, RecipientAccountId, AccountName, AccountUPNSuffix, UserIdentityArn, UserIdentityUserName

ARM