The policy setting allows programs that run on behalf of a user to impersonate that user (or another specified account) so that they can act on behalf of the user. If this user right is required for this kind of impersonation, an unauthorized user will not be able to convince a client to connect-for example, by remote procedure call (RPC) or named pipes-to a service that they have created to impersonate that client, which could elevate the unauthorized user's permissions to administrative or system levels. Services that are started by the Service Control Manager have the built-in Service group added by default to their access tokens. COM servers that are started by the COM infrastructure and configured to run under a specific account also have the Service group added to their access tokens. As a result, these processes are assigned this user right when they are started. Also, a user can impersonate an access token if any of the following conditions exist: The access token that is being impersonated is for this user. The user, in this logon session, logged on to the network with explicit credentials to create the access token. The requested level is less than Impersonate, such as Anonymous or Identify. An attacker with the Impersonate a client after authentication user right could create a service, trick a client to make them connect to the service, and then impersonate that client to elevate the attacker's level of access to that of the client. The recommended state for this setting is: Administrators, LOCAL SERVICE, NETWORK SERVICE, SERVICE. Note: This user right is considered a 'sensitive privilege' for the purposes of auditing. Note #2: A Member Server with Microsoft SQL Server and its optional 'Integration Services' component installed will require a special exception to this recommendation for additional SQL-generated entries to be granted this user right. Rationale: An attacker with the Impersonate a client after authentication user right could create a service, trick a client to make them connect to the service, and then impersonate that client to elevate the attacker's level of access to that of the client.
To establish the recommended configuration via GP, configure the following UI path: Computer Configuration\Policies\Windows Settings\Security Settings\Local Policies\User Rights Assignment\Impersonate a client after authentication Impact: In most cases this configuration will have no impact. If you have installed the Web Server (IIS) Role with Web Services Role Service, you will need to also assign the user right to IIS_IUSRS. Default Value: Administrators, LOCAL SERVICE, NETWORK SERVICE, SERVICE.