NetworkManager-l2tp contains an improper input validation vulnerability that allows local users with VPN connection creation permissions to inject arbitrary pppd directives by supplying mru or mtu property values containing trailing non-numeric content after a valid integer. Attackers can exploit the verbatim write of unvalidated strings into the pppd options file via write_config_option() to inject the plugin directive, causing the privileged pppd process to load an attacker-controlled shared object and achieve arbitrary code execution as root.