Affected versions of CUPS allow for the SetEnv and PassEnv directives to be specified in the cupsd.conf file, which is editable by non-root users using the cupsctl binary. This allows attacker-controlled environment variables to be passed to CUPS backends, some of which are run as root. By passing malicious values in environment variables to affected backends, it is possible to execute an attacker-supplied binary as root, subject to sandbox restrictions. https://nvd.nist.gov/vuln/detail/CVE-2018-4180
