A command injection vulnerability in install package validation subsystem of Juniper Networks Junos OS that may allow a locally authenticated attacker with privileges to execute commands with root privilege. To validate a package in Junos before installation, an administrator executes the command 'request system software add validate-on-host' via the CLI. An attacker with access to this CLI command may be able to exploit this vulnerability. This issue affects Juniper Networks Junos OS: all versions prior to 17.3R3-S10; 17.4 versions prior to 17.4R2-S12, 17.4R3-S3; 18.1 versions prior to 18.1R3-S11; 18.2 versions prior to 18.2R2-S8, 18.2R3-S6; 18.3 versions prior to 18.3R3-S4; 18.4 versions prior to 18.4R1-S8, 18.4R2-S7, 18.4R3-S6; 19.1 versions prior to 19.1R1-S6, 19.1R2-S2, 19.1R3-S3; 19.2 versions prior to 19.2R3-S1; 19.3 versions prior to 19.3R2-S5, 19.3R3-S1; 19.4 versions prior to 19.4R2-S2, 19.4R3-S1; 20.1 versions prior to 20.1R2; 20.2 versions prior to 20.2R1-S2, 20.2R2; 20.3 versions prior to 20.3R1-S1, 20.3R2.