Preventing cross-service confused deputy problems
The confused deputy problem is a security issue where an entity that doesn't have permission to perform an action can coerce a more-privileged entity to perform the action. In AWS, cross-service impersonation can result in the confused deputy problem.
Cross-service impersonation can occur when one service (the calling service) calls another service (the called service). The calling service can be manipulated to use its permissions to act on another customer's resources in a way that it shouldn't have permission to access. To prevent this, AWS provides tools that can help you protect your data for all services with service principals that have been given access to resources in your account. For more information, see The confused deputy problem in the IAM User Guide.
To limit the permissions that Amazon RDS gives another service for a specific resource, we
recommend using the aws:SourceArn
and aws:SourceAccount
global condition context keys in resource policies.
In some cases, the aws:SourceArn
value doesn't contain the account ID, for
example when you use the Amazon Resource Name (ARN) for an Amazon S3 bucket. In these cases, make
sure to use both global condition context keys to limit permissions. In some cases, you use both
global condition context keys and the aws:SourceArn
value contains the account ID.
In these cases, make sure that the aws:SourceAccount
value and the account in the
aws:SourceArn
use the same account ID when they're used in the same policy
statement. If you want only one resource to be associated with the cross-service access, use
aws:SourceArn
. If you want to allow any resource in the specified AWS account
to be associated with the cross-service use, use aws:SourceAccount
.
Make sure that the value of aws:SourceArn
is an ARN for an Amazon RDS resource type.
For more information, see Amazon Resource Names (ARNs) in Amazon RDS.
The most effective way to protect against the confused deputy problem is to use the
aws:SourceArn
global condition context key with the full ARN of the resource. In
some cases, you might not know the full ARN of the resource or you might be specifying multiple
resources. In these cases, use the aws:SourceArn
global context condition key with
wildcards (*
) for the unknown portions of the ARN. An example is
arn:aws:rds:*:
. 123456789012
:*
The following example shows how you can use the aws:SourceArn
and
aws:SourceAccount
global condition context keys in Amazon RDS to prevent
the confused deputy problem.
{ "Version": "2012-10-17", "Statement": { "Sid": "ConfusedDeputyPreventionExamplePolicy", "Effect": "Allow", "Principal": { "Service": "rds.amazonaws.com" }, "Action": "sts:AssumeRole", "Condition": { "ArnLike": { "aws:SourceArn": "arn:aws:rds:
us-east-1
:123456789012
:db:mydbinstance
" }, "StringEquals": { "aws:SourceAccount": "123456789012
" } } } }
For more examples of policies that use the aws:SourceArn
and aws:SourceAccount
global condition context keys, see
the following sections:
-
Granting permissions to publish notifications to an Amazon SNS topic
-
Setting up access to an Amazon S3 bucket (PostgreSQL import)
-
Setting up access to an Amazon S3 bucket (PostgreSQL export)