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Event Information

  • The PutBucketCors event in AWS for S3 refers to an action taken to configure Cross-Origin Resource Sharing (CORS) for a specific S3 bucket.
  • CORS allows web applications running in one domain to access resources (such as images, fonts, or JavaScript) from another domain. It is a security mechanism implemented by web browsers to protect against cross-origin requests.
  • When the PutBucketCors event is triggered, it means that the CORS configuration for the S3 bucket has been updated, allowing or restricting access to the bucket’s resources from different domains.

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Examples

  • Exposing sensitive data: If the CORS configuration allows requests from any origin, it may expose sensitive data stored in the S3 bucket to unauthorized users. This can lead to data breaches and compromise the security of the system.

  • Cross-origin resource sharing attacks: Improperly configured CORS settings can allow malicious websites to make unauthorized requests to the S3 bucket, leading to potential cross-origin resource sharing attacks. This can result in unauthorized access, data manipulation, or denial of service.

  • Information disclosure: If the CORS configuration allows requests from unauthorized origins, it may inadvertently disclose information about the system’s architecture, infrastructure, or internal resources. This information can be exploited by attackers to plan targeted attacks or gain unauthorized access to the system.

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Remediation

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Using Console

  1. Enable versioning for S3 buckets:

    • Open the AWS Management Console and navigate to the S3 service.
    • Select the desired bucket and click on the “Properties” tab.
    • Under the “Versioning” section, click on “Edit”.
    • Select “Enable versioning” and click on “Save changes”.

  2. Enable server access logging for S3 buckets:

    • Open the AWS Management Console and go to the S3 service.
    • Select the target bucket and click on the “Properties” tab.
    • Under the “Server access logging” section, click on “Edit”.
    • Enable server access logging by selecting the target bucket for logging and specifying a target prefix for log files.
    • Click on “Save changes” to enable server access logging.

  3. Enable cross-region replication for S3 buckets:

    • Open the AWS Management Console and navigate to the S3 service.
    • Select the source bucket and click on the “Management” tab.
    • Under the “Replication” section, click on “Add rule”.
    • Configure the replication rule by selecting the destination bucket, specifying the replication options, and setting the IAM role for replication.
    • Click on “Save changes” to enable cross-region replication for the S3 bucket.

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Using CLI

  1. Enable versioning for S3 buckets:

    • Command: aws s3api put-bucket-versioning --bucket <bucket-name> --versioning-configuration Status=Enabled

  2. Restrict public access to S3 buckets:

    • Command: aws s3api put-public-access-block --bucket <bucket-name> --public-access-block-configuration "BlockPublicAcls=true,IgnorePublicAcls=true,BlockPublicPolicy=true,RestrictPublicBuckets=true"

  3. Enable server-side encryption for S3 buckets:

    • Command: aws s3api put-bucket-encryption --bucket <bucket-name> --server-side-encryption-configuration '{"Rules": [{"ApplyServerSideEncryptionByDefault": {"SSEAlgorithm": "AES256"}}]}'

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Using Python

  1. Enable server-side encryption for S3 buckets:
    • Use the boto3 library in Python to interact with the AWS S3 service.
    • Iterate through all the S3 buckets using the list_buckets() method.
    • For each bucket, check if server-side encryption is enabled using the get_bucket_encryption() method.
    • If encryption is not enabled, use the put_bucket_encryption() method to enable server-side encryption.
import boto3

s3_client = boto3.client('s3')

def enable_s3_encryption():
    response = s3_client.list_buckets()
    for bucket in response['Buckets']:
        bucket_name = bucket['Name']
        encryption = s3_client.get_bucket_encryption(Bucket=bucket_name)
        if 'ServerSideEncryptionConfiguration' not in encryption:
            s3_client.put_bucket_encryption(
                Bucket=bucket_name,
                ServerSideEncryptionConfiguration={
                    'Rules': [
                        {
                            'ApplyServerSideEncryptionByDefault': {
                                'SSEAlgorithm': 'AES256'
                            }
                        }
                    ]
                }
            )
  1. Enable versioning for S3 buckets:
    • Use the boto3 library in Python to interact with the AWS S3 service.
    • Iterate through all the S3 buckets using the list_buckets() method.
    • For each bucket, check if versioning is enabled using the get_bucket_versioning() method.
    • If versioning is not enabled, use the put_bucket_versioning() method to enable versioning.
import boto3

s3_client = boto3.client('s3')

def enable_s3_versioning():
    response = s3_client.list_buckets()
    for bucket in response['Buckets']:
        bucket_name = bucket['Name']
        versioning = s3_client.get_bucket_versioning(Bucket=bucket_name)
        if 'Status' not in versioning or versioning['Status'] != 'Enabled':
            s3_client.put_bucket_versioning(
                Bucket=bucket_name,
                VersioningConfiguration={
                    'Status': 'Enabled'
                }
            )
  1. Enable logging for S3 buckets:
    • Use the boto3 library in Python to interact with the AWS S3 service.
    • Iterate through all the S3 buckets using the list_buckets() method.
    • For each bucket, check if logging is enabled using the get_bucket_logging() method.
    • If logging is not enabled, use the put_bucket_logging() method to enable logging.
import boto3

s3_client = boto3.client('s3')

def enable_s3_logging():
    response = s3_client.list_buckets()
    for bucket in response['Buckets']:
        bucket_name = bucket['Name']
        logging = s3_client.get_bucket_logging(Bucket=bucket_name)
        if 'LoggingEnabled' not in logging:
            s3_client.put_bucket_logging(
                Bucket=bucket_name,
                BucketLoggingStatus={
                    'LoggingEnabled': {
                        'TargetBucket': 'your-logging-bucket',
                        'TargetPrefix': 'logs/'
                    }
                }
            )

Note: Replace 'your-logging-bucket' with the name of the bucket where you want to store the logs.