An administrative role-based access control (ARBAC) model specifies administrative policies over a role-based access control(RBAC) system, where an administrative permission may change an RBAC policy by updating permissions assigned to roles, or assigning/revoking users to/from roles. Consequently, enforcing ARBAC policies over an active access controller while some users are using protected resources would result in conflicts: a policy may be in effect in the RBAC system while being updated by an ARBAC operation. Towards solving this concurrency problem, we propose a session-aware administrative model for RBAC. We show how the concurrency problem can be resolved by enhancing the eXtensible Access Control Markup Language (XACML) reference implementation.In order to do so, we develop an XACML-ARBAC profile to specify ARBAC policies, and enforce these polices by building an ARBAC enforcement module and a session administrative module. The former synchronizes with the evaluation of access control requests. The latter revokes conflicting ongoing user sessions immediately prior to enforcing administrative operations. Experimental studies show reasonable performance characteristics of our initial enhancement to Sun's reference implementation.