A command injection vulnerability in Nokogiri v1.10.3 and earlier allows commands to be executed in a subprocess by Ruby's Kernel.open method. Processes are vulnerable only if the undocumented method Nokogiri::CSS::Tokenizer#load_file is being passed untrusted user input. This vulnerability appears in code generated by the Rexical gem versions v1.0.6 and earlier. Rexical is used by Nokogiri to generate lexical scanner code for parsing CSS queries.