Security Hub controls for AWS KMS
These AWS Security Hub controls evaluate the AWS Key Management Service (AWS KMS) service and resources.
These controls may not be available in all AWS Regions. For more information, see Availability of controls by Region.
[KMS.1] IAM customer managed policies should not allow decryption actions on all KMS keys
Related requirements: NIST.800-53.r5 AC-2, NIST.800-53.r5 AC-2(1), NIST.800-53.r5 AC-3, NIST.800-53.r5 AC-3(15), NIST.800-53.r5 AC-3(7), NIST.800-53.r5 AC-5, NIST.800-53.r5 AC-6, NIST.800-53.r5 AC-6(3)
Category: Protect > Secure access management
Severity: Medium
Resource type:
AWS::IAM::Policy
AWS Config rule:
iam-customer-policy-blocked-kms-actions
Schedule type: Change triggered
Parameters:
-
blockedActionsPatterns: kms:ReEncryptFrom, kms:Decrypt(not customizable) -
excludePermissionBoundaryPolicy:True(not customizable)
Checks whether the default version of IAM customer managed policies allow principals to
use the AWS KMS decryption actions on all resources. The control fails if the policy is open
enough to allow kms:Decrypt or kms:ReEncryptFrom actions on all
KMS keys.
The control only checks KMS keys in the Resource element and doesn't take into account any conditionals in the Condition element of a policy. In addition, the control evaluates both attached and unattached customer managed policies. It doesn't check inline policies or AWS managed policies.
With AWS KMS, you control who can use your KMS keys and gain access to your encrypted data.
IAM policies define which actions an identity (user, group, or role) can perform on which
resources. Following security best practices, AWS recommends that you allow least privilege.
In other words, you should grant to identities only the kms:Decrypt or
kms:ReEncryptFrom permissions and only for the keys that are required to perform a
task. Otherwise, the user might use keys that are not appropriate for your data.
Instead of granting permissions for all keys, determine the minimum set of keys that users
need to access encrypted data. Then design policies that allow users to use only those keys. For
example, do not allow kms:Decrypt permission on all KMS keys. Instead, allow
kms:Decrypt only on keys in a particular Region for your account. By adopting the
principle of least privilege, you can reduce the risk of unintended disclosure of your
data.
Remediation
To modify an IAM customer managed policy, see Editing customer managed policies in
the IAM User Guide. When editing your policy, for the Resource field,
provide the Amazon Resource Name (ARN) of the specific key or keys that you want to allow decryption actions on.
[KMS.2] IAM principals should not have IAM inline policies that allow decryption actions on all KMS keys
Related requirements: NIST.800-53.r5 AC-2, NIST.800-53.r5 AC-2(1), NIST.800-53.r5 AC-3, NIST.800-53.r5 AC-3(15), NIST.800-53.r5 AC-3(7), NIST.800-53.r5 AC-5, NIST.800-53.r5 AC-6, NIST.800-53.r5 AC-6(3)
Category: Protect > Secure access management
Severity: Medium
Resource type:
-
AWS::IAM::Group -
AWS::IAM::Role -
AWS::IAM::User
AWS Config rule:
iam-inline-policy-blocked-kms-actions
Schedule type: Change triggered
Parameters:
-
blockedActionsPatterns: kms:ReEncryptFrom, kms:Decrypt(not customizable)
This control checks whether the inline policies that are embedded in your IAM identities
(role, user, or group) allow the AWS KMS decryption and re-encryption actions on all KMS keys. The control fails
if the policy is open enough to allow kms:Decrypt or
kms:ReEncryptFrom actions on all KMS keys.
The control only checks KMS keys in the Resource element and doesn't take into account any conditionals in the Condition element of a policy.
With AWS KMS, you control who can use your KMS keys and gain access to your encrypted data. IAM policies define which actions an identity (user, group, or role) can perform on which resources. Following security best practices, AWS recommends that you allow least privilege. In other words, you should grant to identities only the permissions they need and only for keys that are required to perform a task. Otherwise, the user might use keys that are not appropriate for your data.
Instead of granting permission for all keys, determine the minimum set of keys that users
need to access encrypted data. Then design policies that allow the users to use only those keys.
For example, do not allow kms:Decrypt permission on all KMS keys. Instead, allow
the permission only on specific keys in a specific Region for your account. By adopting the
principle of least privilege, you can reduce the risk of unintended disclosure of your
data.
Remediation
To modify an IAM inline policy, see Editing inline policies in
the IAM User Guide. When editing your policy, for the Resource field,
provide the Amazon Resource Name (ARN) of the specific key or keys that you want to allow decryption actions on.
[KMS.3] AWS KMS keys should not be deleted unintentionally
Related requirements: NIST.800-53.r5 SC-12, NIST.800-53.r5 SC-12(2)
Category: Protect > Data protection > Data deletion protection
Severity: Critical
Resource type:
AWS::KMS::Key
AWS Config rule: kms-cmk-not-scheduled-for-deletion-2 (custom Security Hub rule)
Schedule type: Change triggered
Parameters: None
This control checks whether KMS keys are scheduled for deletion. The control fails if a KMS key is scheduled for deletion.
KMS keys cannot be recovered once deleted. Data encrypted under a KMS key is also permanently unrecoverable if the KMS key is deleted. If meaningful data has been encrypted under a KMS key scheduled for deletion, consider decrypting the data or re-encrypting the data under a new KMS key unless you are intentionally performing a cryptographic erasure.
When a KMS key is scheduled for deletion, a mandatory waiting period is enforced to allow time to reverse the deletion, if it was scheduled in error. The default waiting period is 30 days, but it can be reduced to as short as 7 days when the KMS key is scheduled for deletion. During the waiting period, the scheduled deletion can be canceled and the KMS key will not be deleted.
For additional information regarding deleting KMS keys, see Deleting KMS keys in the AWS Key Management Service Developer Guide.
Remediation
To cancel a scheduled KMS key deletion, see To cancel key deletion under Scheduling and canceling key deletion (console) in the AWS Key Management Service Developer Guide.
[KMS.4] AWS KMS key rotation should be enabled
Related requirements: CIS AWS Foundations Benchmark v3.0.0/3.6, CIS AWS Foundations Benchmark v1.4.0/3.8, CIS AWS Foundations Benchmark v1.2.0/2.8, NIST.800-53.r5 SC-12, NIST.800-53.r5 SC-12(2), NIST.800-53.r5 SC-28(3), PCI DSS v3.2.1/3.6.4, PCI DSS v4.0.1/3.7.4
Category: Protect > Data Protection > Encryption of data-at-rest
Severity: Medium
Resource type:
AWS::KMS::Key
AWS Config rule:
cmk-backing-key-rotation-enabled
Schedule type: Periodic
Parameters: None
AWS KMS enables customers to rotate the backing key, which is key material stored in AWS KMS and is tied to the key ID of the KMS key. It's the backing key that is used to perform cryptographic operations such as encryption and decryption. Automated key rotation currently retains all previous backing keys so that decryption of encrypted data can take place transparently.
CIS recommends that you enable KMS key rotation. Rotating encryption keys helps reduce the potential impact of a compromised key because data encrypted with a new key can't be accessed with a previous key that might have been exposed.
Remediation
To enable KMS key rotation, see How to enable and disable automatic key rotation in the AWS Key Management Service Developer Guide.
[KMS.5] KMS keys should not be publicly accessible
Category: Protect > Secure network configuration > Resources not publicly accessible
Severity: Critical
Resource type:
AWS::KMS::Key
AWS Config rule: kms-key-policy-no-public-access
Schedule type: Change triggered
Parameters: None
This controls checks whether an AWS KMS key is publicly accessible. The control fails if the KMS key is publicly accessible.
Implementing least privilege access is fundamental to reducing security risk and the impact of errors or malicious intent. If a KMS key policy allows access from external accounts, this means third parties will be able to encrypt and decrypt data using keys in your AWS account and it could result in data exfiltration of all services using the key by an insider threat or an attacker.
Remediation
To update a KMS key policy, see Key policies in AWS KMS in the AWS Key Management Service Developer Guide.
