In a Junos Fusion scenario an External Control of Critical State Data vulnerability in the Satellite Device (SD) control state machine of Juniper Networks Junos OS allows an attacker who is able to make physical changes to the cabling of the device to cause a denial of service (DoS). An SD can get rebooted and subsequently controlled by an Aggregation Device (AD) which does not belong to the original Fusion setup and is just connected to an extended port of the SD. To carry out this attack the attacker needs to have physical access to the cabling between the SD and the original AD. This issue affects: Juniper Networks Junos OS 16.1R1 and later versions prior to 18.4R3-S10; 19.1 versions prior to 19.1R3-S7; 19.2 versions prior to 19.2R3-S4. This issue does not affect Juniper Networks Junos OS versions prior to 16.1R1.