fix(template): use bucket ARN for SSE-KMS encryption context#540
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PR #533 scoped kms:EncryptionContext:aws:s3:arn to the object ARN (<bucket>/<BucketKey>). That works for plain SSE-KMS, but the state bucket has BucketKeyEnabled: true, so S3 generates a short-lived bucket-level data key and derives per-object keys locally — the encryption context S3 forwards to KMS is the bucket ARN, not the object ARN. The condition therefore never matched at runtime and every sync failed with: AccessDenied: ... is not authorized to perform: kms:Decrypt on resource: arn:aws:kms:...:key/... because no identity-based policy allows the kms:Decrypt action (IAM reports a condition-mismatched Allow as "not allowed".) Change both KMSGetDataPolicy and KMSDecryptPolicy to pin the bucket ARN. The role can still only reach the single state object via the S3ObjectPolicy ARN scoping; kms:ViaService still forces all KMS access through S3. Also update docs/Whats-New.md to describe the correct behavior and link to the S3 Bucket Keys docs. Refs: #521, #533 Ref: https://docs.aws.amazon.com/AmazonS3/latest/userguide/bucket-key.html Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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Summary
AccessDenied … kms:Decrypt … no identity-based policy allows the kms:Decrypt action.kms:EncryptionContext:aws:s3:arnto the object ARN, but the state bucket hasBucketKeyEnabled: true. With Bucket Keys enabled, S3 generates a short-lived bucket-level data key and derives per-object keys locally — the encryption context S3 forwards to KMS is the bucket ARN, never the object ARN. The condition therefore never matched, and IAM reports a condition-mismatchedAllowas "not allowed".KMSGetDataPolicyandKMSDecryptPolicynow pin the bucket ARN. The role still cannot reach any other object (theS3ObjectPolicyARN scoping handles that), andkms:ViaServicestill forces all KMS access through S3.docs/Whats-New.mdto describe the correct behavior and link to the AWS S3 Bucket Keys docs.Observed error (before this fix)
Test plan
template.yaml.rate(15 minutes)invocation) and confirm the sync completes without thekms:DecryptAccessDenied.kms:Decryptcall from S3 carrieskms:EncryptionContext:aws:s3:arn = arn:aws:s3:::<bucket>(bucket ARN, no object suffix) — i.e. the new condition matches what S3 actually sends.S3ObjectPolicy, not the KMS condition).Refs: #521, #533
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