AWS IAM Default Policy Version Modification

The modification of the default AWS IAM policy version can be an indicator of malicious activity, potentially performed by an insider threat or an attacker who has gained unauthorized access to an AWS account. While the provided source material lacks specific details on observed campaigns, the ability to modify the default policy version allows for subtle changes to permissions that may go unnoticed. An attacker could revert to a less restrictive version of a policy or introduce a new, permissive version as the default, thereby weakening the security posture of the AWS environment. This can facilitate privilege escalation, data exfiltration, or other malicious activities. Detecting such modifications is crucial for maintaining the integrity and security of AWS environments.

Attack Chain

1. Attacker gains access to AWS Management Console or uses compromised AWS CLI credentials.
2. Attacker identifies a target IAM policy to modify, querying IAM policies to find a suitable target.
3. Attacker retrieves the current default policy version ARN using AWS API calls.
4. Attacker crafts a modified IAM policy version with reduced permissions or unintended access.
5. Attacker creates a new IAM policy version using the AWS API, while keeping the original intact.
6. Attacker uses the aws iam set-default-policy-version command to set the newly crafted policy version as the default.
7. Legitimate users or services relying on the IAM policy now operate under the modified (potentially weakened) permissions.
8. Attacker leverages the broadened permissions for lateral movement, data access, or other malicious objectives.

Impact

Successful modification of the default IAM policy version can lead to privilege escalation, unauthorized access to sensitive data, and potential disruption of services relying on the affected policy. The impact depends on the scope of the policy and the permissions altered. A successful attack can affect multiple AWS services and resources governed by the modified policy. The change can be subtle and persist for a long time if not detected, leading to significant data breaches or service outages.