A denial of service vulnerability in the telnetd service on Junos OS allows remote unauthenticated users to cause high CPU usage which may affect system performance. Affected releases are Juniper Networks Junos OS: 12.1X46 versions prior to 12.1X46-D81 on SRX Series; 12.3 versions prior to 12.3R12-S11; 12.3X48 versions prior to 12.3X48-D80 on SRX Series; 15.1 versions prior to 15.1R7; 15.1X49 versions prior to 15.1X49-D150, 15.1X49-D160 on SRX Series; 15.1X53 versions prior to 15.1X53-D59 on EX2300/EX3400 Series; 15.1X53 versions prior to 15.1X53-D68 on QFX10K Series; 15.1X53 versions prior to 15.1X53-D235 on QFX5200/QFX5110 Series; 15.1X53 versions prior to 15.1X53-D495 on NFX Series; 16.1 versions prior to 16.1R4-S12, 16.1R6-S6, 16.1R7; 16.2 versions prior to 16.2R2-S7, 16.2R3; 17.1 versions prior to 17.1R2-S9, 17.1R3; 17.2 versions prior to 17.2R2-S6, 17.2R3; 17.2X75 versions prior to 17.2X75-D100; 17.3 versions prior to 17.3R2-S4, 17.3R3; 17.4 versions prior to 17.4R1-S5, 17.4R2; 18.2X75 versions prior to 18.2X75-D5.