The shell-quote package before 1.7.3 for Node.js allows command injection. An attacker can inject unescaped shell metacharacters through a regex designed to support Windows drive letters. If the output of this package is passed to a real shell as a quoted argument to a command with `exec()`, an attacker can inject arbitrary commands. This is because the Windows drive letter regex character class is `[A-z]` instead of the correct `[A-Za-z]`. Several shell metacharacters exist in the space between capital letter Z and lower case letter a, such as the backtick character.