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العربيةDecrypt with a KMS key granted to an external AWS account
A KMS key's policy grants an external AWS account use of the key..
No IAM permission is needed. The exposure is in the resource's own configuration, so anyone the policy names, or everyone when it is public, can reach it.
This is a configuration exposure, not a permission. A KMS key's policy grants an external AWS account use of the key. Anyone the policy allows, or everyone when it is public, can reach it with no IAM access of their own.
Why it is dangerous
A KMS key's policy grants an external AWS account with no narrowing condition; an attacker controlling that account can use the key (kms:Decrypt) directly.
In MITRE ATT&CK terms this maps to T1530, Data from Cloud Storage, under the collection tactic. AWS records it in CloudTrail as kms:GetKeyPolicy / Decrypt (CloudTrail). The call is quiet against normal activity, so it is easy to miss without a rule for it.
Detection
kms:GetKeyPolicy / Decrypt (CloudTrail)Prerequisites
Control of the named external AWS account; the key policy grants it with no narrowing condition.
MITRE ATT&CK
T1530 · Data from Cloud StorageTactic
Collection
A control that would remove it: Scope the grant to your org (aws:PrincipalOrgID) / a SourceArn, or remove the external principal.
Whether to apply it depends on how the permission is used in your environment, so it is a business decision rather than an automatic fix. The same permission can be load-bearing in one account and pure risk in another.
Pathbreak confirms whether this path resolves in your account, ranks it against the others by how much it opens up, and uses your threat model and business context to show which paths are worth cutting.
Questions
What does this configuration allow?
A KMS key's policy grants an external AWS account use of the key.
Does this need any IAM permission?
No. It is a configuration exposure. Anyone the resource policy names, or everyone when it is public, can reach it without holding any permission of their own.
How is decrypt with a KMS key granted to an external AWS account detected?
Watch for kms:GetKeyPolicy / Decrypt (CloudTrail) in CloudTrail. The call is quiet against normal activity, so it is easy to miss without a rule for it.
How do you break this path?
A control that would remove it is: Scope the grant to your org (aws:PrincipalOrgID) / a SourceArn, or remove the external principal. Whether to apply it depends on how the permission is used in your account, so it is a business decision rather than an automatic fix.
Which MITRE ATT&CK technique is this?
T1530, Data from Cloud Storage, under the collection tactic.
Related paths
References
Find this in your own account
We run a read-only scan of one AWS account and show you which of these paths exist, ranked by blast radius, with the change that breaks each one. First validated paths within the hour.