If REST API is enabled, the Junos OS login credentials are vulnerable to brute force attacks.

The high default connection limit of the REST API may allow an attacker to brute-force passwords using advanced scripting techniques.  Additionally, administrators who do not enforce a strong password policy can increase the likelihood of success from brute force attacks.
Affected releases are Juniper Networks Junos OS:
14.1X53 versions prior to 14.1X53-D49;
15.1 versions prior to 15.1F6-S12, 15.1R7-S3;
15.1X49 versions prior to 15.1X49-D160;
15.1X53 versions prior to 15.1X53-D236, 15.1X53-D495, 15.1X53-D591, 15.1X53-D69;
16.1 versions prior to 16.1R3-S10, 16.1R4-S12, 16.1R6-S6, 16.1R7-S3;
16.1X65 versions prior to 16.1X65-D49;
16.2 versions prior to 16.2R2-S7;
17.1 versions prior to 17.1R2-S10, 17.1R3;
17.2 versions prior to 17.2R1-S8, 17.2R3-S1;
17.3 versions prior to 17.3R3-S2;
17.4 versions prior to 17.4R1-S6, 17.4R2-S2;
18.1 versions prior to 18.1R2-S4, 18.1R3-S1;
18.2 versions prior to 18.2R1-S5;
18.2X75 versions prior to 18.2X75-D30;
18.3 versions prior to 18.3R1-S1.

If REST API is enabled, the Junos OS login credentials are vulnerable to brute force attacks. The high default connection limit of the REST API may allow an attacker to brute-force passwords using advanced scripting techniques. Additionally, administrators who do not enforce a strong password policy can increase the likelihood of success from brute force attacks. Affected releases are Juniper Networks Junos OS: 14.1X53 versions prior to 14.1X53-D49; 15.1 versions prior to 15.1F6-S12, 15.1R7-S3; 15.1X49 versions prior to 15.1X49-D160; 15.1X53 versions prior to 15.1X53-D236, 15.1X53-D495, 15.1X53-D591, 15.1X53-D69; 16.1 versions prior to 16.1R3-S10, 16.1R4-S12, 16.1R6-S6, 16.1R7-S3; 16.1X65 versions prior to 16.1X65-D49; 16.2 versions prior to 16.2R2-S7; 17.1 versions prior to 17.1R2-S10, 17.1R3; 17.2 versions prior to 17.2R1-S8, 17.2R3-S1; 17.3 versions prior to 17.3R3-S2; 17.4 versions prior to 17.4R1-S6, 17.4R2-S2; 18.1 versions prior to 18.1R2-S4, 18.1R3-S1; 18.2 versions prior to 18.2R1-S5; 18.2X75 versions prior to 18.2X75-D30; 18.3 versions prior to 18.3R1-S1.