Juniper Junos 10.4 before 10.4S15, 11.4 before 11.4R9, 11.4X27 before 11.4X27.44, 12.1 before 12.1R7, 12.1X44 before 12.1X44-D20, 12.1X45 before 12.1X45-D15, 12.2 before 12.2R6, 12.3 before 12.3R3, 13.1 before 13.1R3, and 13.2 before 13.2R1, when Proxy ARP is enabled on an unnumbered interface, allows remote attackers to perform ARP poisoning attacks and possibly obtain sensitive information via a crafted ARP message.