S3 Public Access Block Deleted

Status: Experimental
Severity: medium
Log types: AWS.CloudTrail
Tags: AWS, Defense Evasion, Initial Access
Reference: https://docs.aws.amazon.com/AmazonS3/latest/userguide/access-control-block-public-access.html
Source: github.com/panther-labs/panther-analysis

Detects when S3 bucket public access block configuration is deleted, which could allow unauthorized public access to sensitive data or indicate preparation for data exfiltration.

MITRE ATT&CK coverage

Tactic	Techniques
Initial Access	`T1190` Exploit Public-Facing Application
Stealth	`T1562` Impair Defenses

Rule body yaml

AnalysisType: rule
Filename: aws_s3_delete_public_access_block.py
RuleID: "AWS.S3.DeletePublicAccessBlock"
DisplayName: "S3 Public Access Block Deleted"
Enabled: true
LogTypes:
  - AWS.CloudTrail
Tags:
  - AWS
  - Defense Evasion
  - Initial Access
Reports:
  MITRE ATT&CK:
    - TA0005:T1562
    - TA0001:T1190
Severity: Medium
Status: Experimental
Description: Detects when S3 bucket public access block configuration is deleted, which could allow unauthorized public access to sensitive data or indicate preparation for data exfiltration.
Runbook: |
  1. Query CloudTrail for all S3 API calls by the userIdentity:arn on the requestParameters:bucketName in the 24 hours before and after the public access block deletion
  2. Find any PutBucketPolicy or PutBucketAcl events on this bucket in the 1 hour after the deletion to check if the bucket or objects were made public
  3. Search for GetObject events from public IP addresses on this bucket in the 6 hours after the deletion to detect unauthorized data access
Reference: https://docs.aws.amazon.com/AmazonS3/latest/userguide/access-control-block-public-access.html
SummaryAttributes:
  - sourceIpAddress
  - userAgent
  - recipientAccountId
  - p_any_aws_arns
Tests:
  - Name: Public Access Block Deleted Successfully
    ExpectedResult: true
    Log:
      {
        "eventVersion": "1.08",
        "userIdentity":
          {
            "type": "AssumedRole",
            "principalId": "AAAAAAAAAAAAAAAAAAAAA:user_name",
            "arn": "arn:aws:sts::111111111111:assumed-role/sample-role-dreamy-yonath/sample-role-brave-yalow-role-intelligent-brahmagupta-role-beautiful-keldysh-role-happy-easley-role-bold-buck",
            "accountId": "111111111111",
            "accessKeyId": "ASIA-MOCKACCESSKEYID-1",
            "sessionContext":
              {
                "attributes":
                  {
                    "mfaAuthenticated": "false",
                    "creationDate": "2024-01-15T10:30:00Z",
                  },
                "sessionIssuer":
                  {
                    "type": "Role",
                    "principalId": "AAAAAAAAAAAAAAAAAAAAA",
                    "arn": "arn:aws:iam::111111111111:role/sample-role-dreamy-yonath",
                    "accountId": "111111111111",
                    "userName": "AdminRole",
                  },
              },
          },
        "eventTime": "2024-01-15T10:45:23Z",
        "eventSource": "s3.amazonaws.com",
        "eventName": "DeleteBucketPublicAccessBlock",
        "awsRegion": "us-east-1",
        "sourceIPAddress": "1.2.3.4",
        "userAgent": "aws-cli/2.13.0 Python/3.11.4 Linux/5.10.0-1234-aws exe/x86_64.ubuntu.22",
        "requestParameters":
          {
            "bucketName": "corporate-documents",
            "host": "sample-bucket-sweet-kepler.s3.amazonaws.com",
            "publicAccessBlock": "",
          },
        "responseElements": null,
        "requestID": "ABC123DEF456",
        "eventID": "12345678-1234-1234-1234-111111111111",
        "readOnly": false,
        "eventType": "AwsApiCall",
        "managementEvent": true,
        "recipientAccountId": "111111111111",
        "vpcEndpointId": "vpce-1a2b3c4d",
      }
  - Name: Public Access Block Deletion Failed
    ExpectedResult: false
    Log:
      {
        "eventVersion": "1.08",
        "userIdentity":
          {
            "type": "IAMUser",
            "principalId": "AIDAI23HXS4EXAMPLE",
            "arn": "arn:aws:iam::111111111111:user/testuser",
            "accountId": "111111111111",
            "accessKeyId": "AKIA-MOCKACCESSKEYID-1",
          },
        "eventTime": "2024-01-15T10:45:23Z",
        "eventSource": "s3.amazonaws.com",
        "eventName": "DeleteBucketPublicAccessBlock",
        "awsRegion": "us-east-1",
        "sourceIPAddress": "1.2.3.4",
        "userAgent": "aws-cli/2.13.0 Python/3.11.4 Linux/5.10.0-1234-aws exe/x86_64.ubuntu.22",
        "errorCode": "AccessDenied",
        "errorMessage": "Access Denied",
        "requestParameters":
          {
            "bucketName": "corporate-documents",
            "host": "sample-bucket-sweet-kepler.s3.amazonaws.com",
          },
        "responseElements": null,
        "requestID": "ABC123DEF456",
        "eventID": "12345678-1234-1234-1234-111111111111",
        "readOnly": false,
        "eventType": "AwsApiCall",
        "managementEvent": true,
        "recipientAccountId": "111111111111",
      }
  - Name: Different S3 Event
    ExpectedResult: false
    Log:
      {
        "eventVersion": "1.08",
        "userIdentity":
          {
            "type": "AssumedRole",
            "principalId": "AAAAAAAAAAAAAAAAAAAAA:user_name",
            "arn": "arn:aws:sts::111111111111:assumed-role/sample-role-dreamy-yonath/sample-role-brave-yalow-role-intelligent-brahmagupta-role-beautiful-keldysh-role-happy-easley-role-bold-buck",
            "accountId": "111111111111",
            "accessKeyId": "ASIA-MOCKACCESSKEYID-1",
          },
        "eventTime": "2024-01-15T10:45:23Z",
        "eventSource": "s3.amazonaws.com",
        "eventName": "PutBucketPublicAccessBlock",
        "awsRegion": "us-east-1",
        "sourceIPAddress": "1.2.3.4",
        "userAgent": "aws-cli/2.13.0 Python/3.11.4 Linux/5.10.0-1234-aws exe/x86_64.ubuntu.22",
        "requestParameters":
          {
            "bucketName": "corporate-documents",
            "host": "sample-bucket-sweet-kepler.s3.amazonaws.com",
          },
        "responseElements": null,
        "requestID": "ABC123DEF456",
        "eventID": "12345678-1234-1234-1234-111111111111",
        "readOnly": false,
        "eventType": "AwsApiCall",
        "managementEvent": true,
        "recipientAccountId": "111111111111",
      }
  - Name: Non-S3 Event
    ExpectedResult: false
    Log:
      {
        "eventVersion": "1.08",
        "userIdentity":
          {
            "type": "AssumedRole",
            "principalId": "AAAAAAAAAAAAAAAAAAAAA:user_name",
            "arn": "arn:aws:sts::123456789012:assumed-role/AdminRole/user_name",
            "accountId": "123456789012",
            "accessKeyId": "ASIAIOSFODNN7EXAMPLE",
          },
        "eventTime": "2024-01-15T10:45:23Z",
        "eventSource": "ec2.amazonaws.com",
        "eventName": "DeleteBucketPublicAccessBlock",
        "awsRegion": "us-east-1",
        "sourceIPAddress": "203.0.113.42",
        "userAgent": "aws-cli/2.13.0 Python/3.11.4 Linux/5.10.0-1234-aws exe/x86_64.ubuntu.22",
        "requestParameters": {},
        "responseElements": null,
        "requestID": "ABC123DEF456",
        "eventID": "12345678-1234-1234-1234-123456789012",
        "readOnly": false,
        "eventType": "AwsApiCall",
        "managementEvent": true,
        "recipientAccountId": "123456789012",
      }

Detection logic

Condition

not (errorCode is_not_null or errorMessage is_not_null)
eventSource eq "s3.amazonaws.com"
eventName eq "DeleteBucketPublicAccessBlock"

Exclusions

Top-level NOT(...) conjuncts: predicates this rule actively suppresses.

Field	Kind	Excluded values
`errorCode`	is_not_null	(no value, null check)
`errorMessage`	is_not_null	(no value, null check)

Indicators

Each row is a field, operator, and value that the rule matches. The corpus column counts how many other rules in the catalog look for the same combination: high numbers point to widely-used, community-vetted indicators. Blank or 1 shows that the indicator is specific to this rule.

Field	Kind	Values
`eventName`	eq	`DeleteBucketPublicAccessBlock`
`eventSource`	eq	`s3.amazonaws.com`

Output fields

Fields the rule emits when it matches. Chronicle authors list these in the outcome block; they appear on the detection and $risk_score drives alerting. Sentinel / Defender XDR rules build them up through project / summarize / extend stages. Sentinel maps these into alert fields via entityMappings and customDetails; Defender XDR custom detections surface them as alert fields directly.

Field	Source
`eventName`
`eventSource`
`awsRegion`
`recipientAccountId`
`sourceIPAddress`
`userAgent`
`userIdentity`
`actor_user`
`bucketName`	`requestParameters.bucketName`

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`-op:val`	Exclude matches; works on most operators but not `type:`/`like:`/`has:`/`no:` (use `no:<flag>` to exclude a rule flag): `tactic:execution -vendor:splunk`. Standalone `-kind:`/`-field:`/`-value:` drop every rule carrying a matching predicate leaf (`type:rules -kind:is_null`)
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