Cisco Firewall Services Module (aka FWSM) 3.1 before 3.1(21) 3.2 before 3.2(22) 4.0 before 4.0(16) and 4.1 before 4.1(7) when certain authentication configurations are used allows remote attackers to cause a denial of service (module crash) by making many authentication requests for network access aka Bug ID CSCtn15697.