Cis AWS Foundations 4.2

Ensure CloudTrail log file validation is enabled

Description

CloudTrail log file validation creates a digitally signed digest file containing a hash of each log that CloudTrail writes to S3. These digest files can be used to determine whether a log file was changed, deleted, or remained unchanged after CloudTrail delivered the log. It is recommended that file validation be enabled for all CloudTrails.

Rationale

Enabling log file validation will provide additional integrity checks for CloudTrail logs.

Impact

N/A

Audit Procedure

Using AWS Console

1. Sign in to the AWS Management Console and open the IAM console at https://console.aws.amazon.com/cloudtrail.
2. Click on Trails in the left navigation pane.
3. For every trail:
   • Click a trail via the link in the Name column.
   • Under the General details section, ensure log file validation is set to Enabled.

Using AWS CLI

List all trails:

aws cloudtrail describe-trails

Ensure LogFileValidationEnabled is set to true for each trail.

Expected Result

All CloudTrail trails have LogFileValidationEnabled set to true.

Remediation

Using AWS Console

1. Sign in to the AWS Management Console and open the IAM console at https://console.aws.amazon.com/cloudtrail.
2. Click on Trails in the left navigation pane.
3. Click on the target trail.
4. Within the General details section, click edit.
5. Under Advanced settings, check the enable box under Log file validation.
6. Click Save changes.

Using AWS CLI

Enable log file validation on a trail:

aws cloudtrail update-trail --name <trail_name> --enable-log-file-validation

Note that periodic validation of logs using these digests can be carried out by running the following command:

aws cloudtrail validate-logs --trail-arn <trail_arn> --start-time <start_time> --end-time <end_time>

Default Value

By default, CloudTrail log file validation is not enabled. This means that while logs are still delivered to the designated S3 bucket, there is no mechanism in place to verify their integrity. Without validation, it is not possible to detect if log files have been altered, deleted, or tampered with after delivery.

References

1. https://docs.aws.amazon.com/awscloudtrail/latest/userguide/cloudtrail-log-file-validation-enabling.html
2. CCE-78914-9

CIS Controls

MITRE ATT&CK Mappings

Profile

Level 2 | Automated