Juniper Junos before 10.4 before 10.4R16, 11.4 before 11.4R8, 12.1R before 12.1R7, 12.1X44 before 12.1X44-D20, and 12.1X45 before 12.1X45-D10 on SRX Series service gateways, when used as a UAC enforcer and captive portal is enabled, allows remote attackers to cause a denial of service (flowd crash) via a crafted HTTP message.