> ## Documentation Index
> Fetch the complete documentation index at: https://cloudanix.com/docs/llms.txt
> Use this file to discover all available pages before exploring further.

# EventBus Should Not Allow Cross Account Access

### More Info:

AWS CloudWatch event buses should not allow unknown cross-account access for delivery of events.

### Risk Level

High

### Address

Security

### Compliance Standards

AWSWAF

### Triage and Remediation

<Tabs>
  <Tab title="Remediation">
    ### Remediation

    <AccordionGroup>
      <Accordion title="Using Console" defaultOpen="true">
        To remediate the "EventBus Should Not Allow Cross Account Access" misconfiguration in AWS using the AWS console, follow these steps:

        1. Login to the AWS Management Console.
        2. Navigate to the Amazon EventBridge service.
        3. Select the Event Bus that is allowing cross-account access.
        4. Click on the "Permissions" tab.
        5. In the "Event bus policies" section, click on the "Edit" button.
        6. Remove any statements that grant cross-account access to the Event Bus.
        7. Add a new statement that only allows access from the AWS account(s) that require access to the Event Bus.
        8. Click on the "Save" button to apply the changes.

        After following these steps, the Event Bus will no longer allow cross-account access and will only allow access from the specified AWS account(s).

        #
      </Accordion>

      <Accordion title="Using CLI">
        To remediate the "EventBus Should Not Allow Cross Account Access" misconfiguration in AWS using AWS CLI, follow these steps:

        1. Open your terminal or command prompt and ensure that you have the AWS CLI installed and configured with the appropriate credentials.

        2. Run the following command to list all the Amazon EventBridge event buses in your AWS account:

           ```
           aws events list-event-buses
           ```

        3. Identify the event bus that is allowing cross-account access.

        4. Run the following command to modify the event bus policy and restrict cross-account access:

           ```
           aws events put-policy --event-bus-name <event-bus-name> --policy '{"Statement":[{"Sid":"RestrictCrossAccountAccess","Effect":"Deny","Principal":"*","Action":"events:PutEvents","Resource":"arn:aws:events:<region>:<account-id>:event-bus/<event-bus-name>"}]}'
           ```

           Replace `<event-bus-name>` with the name of the event bus that is allowing cross-account access, `<region>` with the AWS region where the event bus is located, and `<account-id>` with your AWS account ID.

        5. Verify that the policy has been updated by running the following command:

           ```
           aws events describe-event-bus --name <event-bus-name>
           ```

           The output should show the updated policy with the `Deny` statement.

        6. Repeat steps 3-5 for any other event buses that are allowing cross-account access.

        By following these steps, you have successfully remediated the "EventBus Should Not Allow Cross Account Access" misconfiguration in AWS using AWS CLI.
      </Accordion>

      <Accordion title="Using Python">
        To remediate the misconfiguration "EventBus Should Not Allow Cross Account Access" in AWS, you can follow the below steps in Python:

        1. Create a new EventBridge event bus policy that allows access only to the specific AWS account that should have access to the event bus.

        ```python theme={null}
        import boto3
        import json

        eventbridge = boto3.client('events')

        account_id = boto3.client('sts').get_caller_identity().get('Account')

        policy = {
            "Version": "2012-10-17",
            "Statement": [
                {
                    "Sid": "AllowAccountAccess",
                    "Effect": "Allow",
                    "Principal": {
                        "AWS": f"arn:aws:iam::{account_id}:root"
                    },
                    "Action": "events:*",
                    "Resource": "arn:aws:events:us-east-1:<account_id>:event-bus/default"
                }
            ]
        }

        policy_json = json.dumps(policy)

        eventbridge.put_permission(
            Action='events:PutEvents',
            Principal='*',
            StatementId='AllowAccountAccess',
            Condition={
                'ArnEquals': {
                    'aws:SourceArn': f'arn:aws:events:us-east-1:<account_id>:event-bus/default'
                }
            }
        )

        eventbridge.put_event_bus_policy(
            EventBusName='default',
            Policy=policy_json
        )
        ```

        2. Remove any existing event bus policies that allow cross-account access.

        ```python theme={null}
        policy = {
            "Version": "2012-10-17",
            "Statement": [
                {
                    "Sid": "DenyCrossAccountAccess",
                    "Effect": "Deny",
                    "Principal": "*",
                    "Action": "events:*",
                    "Resource": "arn:aws:events:us-east-1:<account_id>:event-bus/default",
                    "Condition": {
                        "StringNotEquals": {
                            "aws:PrincipalAccount": "<account_id>"
                        }
                    }
                }
            ]
        }

        policy_json = json.dumps(policy)

        eventbridge.put_event_bus_policy(
            EventBusName='default',
            Policy=policy_json
        )
        ```

        3. Verify that the event bus policy now only allows access to the specific AWS account that should have access to the event bus.

        ```python theme={null}
        policy = eventbridge.describe_event_bus(
            Name='default'
        )['Policy']

        print(policy)
        ```

        This should remediate the "EventBus Should Not Allow Cross Account Access" misconfiguration in AWS.
      </Accordion>
    </AccordionGroup>
  </Tab>
</Tabs>

### Additional Reading:

* [https://docs.aws.amazon.com/AmazonCloudWatch/latest/events/CloudWatchEvents-CrossAccountEventDelivery.html](https://docs.aws.amazon.com/AmazonCloudWatch/latest/events/CloudWatchEvents-CrossAccountEventDelivery.html)