An improper neutralization of special elements used in an OS Command ('OS Command Injection') vulnerabilities [CWE-78] in Telnet login components of FortiTester 2.3.0 through 3.9.1, 4.0.0 through 4.2.0, 7.0.0 through 7.1.0 may allow an unauthenticated remote attacker to execute arbitrary command in the underlying shell.