# Cross-service confused deputy prevention


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 Amazon, 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 it should not otherwise have permission to access. To prevent this, Amazon provides tools that help you protect your data for all services with service principals that have been given access to resources in your account. 

We recommend using the [https://docs.amazonaws.cn/IAM/latest/UserGuide/reference_policies_condition-keys.html#condition-keys-sourcearn](https://docs.amazonaws.cn/IAM/latest/UserGuide/reference_policies_condition-keys.html#condition-keys-sourcearn), [https://docs.amazonaws.cn/IAM/latest/UserGuide/reference_policies_condition-keys.html#condition-keys-sourceaccount](https://docs.amazonaws.cn/IAM/latest/UserGuide/reference_policies_condition-keys.html#condition-keys-sourceaccount), [https://docs.amazonaws.cn/IAM/latest/UserGuide/reference_policies_condition-keys.html#condition-keys-sourceorgid](https://docs.amazonaws.cn/IAM/latest/UserGuide/reference_policies_condition-keys.html#condition-keys-sourceorgid), and [https://docs.amazonaws.cn/IAM/latest/UserGuide/reference_policies_condition-keys.html#condition-keys-sourceorgpaths](https://docs.amazonaws.cn/IAM/latest/UserGuide/reference_policies_condition-keys.html#condition-keys-sourceorgpaths) global condition context keys in resource policies to limit the permissions that xraylong gives another service to the resource. Use `aws:SourceArn` to associate only one resource with cross-service access. Use `aws:SourceAccount` to let any resource in that account be associated with the cross-service use. Use `aws:SourceOrgID` to allow any resource from any account within an organization be associated with the cross-service use. Use `aws:SourceOrgPaths` to associate any resource from accounts within an Amazon Organizations path with the cross-service use. For more information about using and understanding paths, see [Understand the Amazon Organizations entity path](https://docs.amazonaws.cn/IAM/latest/UserGuide/access_policies_access-advisor-view-data-orgs.html#access_policies_access-advisor-viewing-orgs-entity-path).

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. If you don't know the full ARN of the resource or if you are specifying multiple resources, use the `aws:SourceArn` global context condition key with wildcard characters (`*`) for the unknown portions of the ARN. For example, `arn:aws-cn:servicename:*:123456789012:*`. 

If the `aws:SourceArn` value does not contain the account ID, such as an Amazon S3 bucket ARN, you must use both `aws:SourceAccount` and `aws:SourceArn` to limit permissions.

To protect against the confused deputy problem at scale, use the `aws:SourceOrgID` or `aws:SourceOrgPaths` global condition context key with the organization ID or organization path of the resource in your resource-based policies. Policies that include the `aws:SourceOrgID` or `aws:SourceOrgPaths` key will automatically include the correct accounts and you don't have to manually update the policies when you add, remove, or move accounts in your organization.

The following example shows how you can use the `aws:SourceArn` and `aws:SourceAccount` global condition context keys in xray to prevent the confused deputy problem.

```
{
      "Sid": "BlockCrossAccountUnlessSameSource",
      "Effect": "Deny",
      "Principal": {
        "AWS": "*"
      },
      "Action": [
        "kms:Decrypt",
        "kms:GenerateDataKeyWithoutPlaintext"
      ],
      "Resource": "*",
      "Condition": {
        "StringNotEquals": {
          "aws:PrincipalAccount": "123456789012",
          "aws:SourceAccount": "123456789012"
        },
        "ArnNotLike": {
          "aws:SourceArn": "arn:*:*:*:123456789012:*"
        }
      }
    }
```