A vulnerability in the BGP FlowSpec implementation may cause a Juniper Networks Junos OS device to terminate an established BGP session upon receiving a specific BGP FlowSpec advertisement. The BGP NOTIFICATION message that terminates an established BGP session is sent toward the peer device that originally sent the specific BGP FlowSpec advertisement. This specific BGP FlowSpec advertisement received from a BGP peer might get propagated from a Junos OS device running the fixed release to another device that is vulnerable causing BGP session termination downstream. This issue affects IPv4 and IPv6 BGP FlowSpec deployment. This issue affects Juniper Networks Junos OS: 12.3; 12.3X48 on SRX Series; 14.1X53 on EX and QFX Series; 15.1 versions prior to 15.1R7-S5; 15.1F versions prior to 15.1F6-S13; 15.1X49 versions prior to 15.1X49-D180 on SRX Series; 15.1X53 versions prior to 15.1X53-D238 on QFX5200/QFX5110; 15.1X53 versions prior to 15.1X53-D497 on NFX Series; 15.1X53 versions prior to 15.1X53-D592 on EX2300/EX3400; 16.1 versions prior to 16.1R7-S7; 17.1 versions prior to 17.1R2-S12, 17.1R3; 17.2 versions prior to 17.2R2-S7, 17.2R3; 17.2X75 versions prior to 17.2X75-D102, 17.2X75-D110, 17.2X75-D44; 17.3 versions prior to 17.3R2-S5, 17.3R3-S5; 17.4 versions prior to 17.4R1-S8, 17.4R2; 18.1 versions prior to 18.1R2-S4, 18.1R3; 18.2X75 versions prior to 18.2X75-D20.