An OS Command Injection vulnerability was discovered in the Google Cloud DNS validation module of the OPNsense os-acme-client plugin through 4.17. The DnsGcloud::prepare() method decodes the dns_gcloud_key model field and directly interpolates the string fields gcloud_account and gcloud_project into a shell command passed to proc_open() via LeUtils::run_shell_command() without any validation or escaping. A remote authenticated user with privileges to issue or renew certificates through the WebGUI/API can achieve arbitrary code execution as root.