Details for this vulnerability have not been published by NIST at this point. Descriptions from software vendor advisories for this issue are provided below.
Nokogiri GitHub release:
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. The underlying
vulnerability was addressed in Rexical v1.0.7 and Nokogiri upgraded to
this version of Rexical in Nokogiri v1.10.4.