The L2TP packet processing functionality in Juniper Netscreen and ScreenOS Firewall products with ScreenOS before 6.3.0r13-dnd1, 6.3.0r14 through 6.3.0r18 before 6.3.0r18-dnc1, and 6.3.0r19 allows remote attackers to cause a denial of service via a crafted L2TP packet.