Not running, but supported. You can check your app with:

    bin/rails runner '
      require "vips"
      puts "ruby-vips #{Vips::VERSION}  libvips #{Vips.version(0)}.#{Vips.version(1)}.#{Vips.version(2)}"
      begin
        Vips::Operation.new("matload")
        puts "matload PRESENT - this build can reach libmatio"
      rescue Vips::Error
        puts "matload ABSENT - this build cannot reach libmatio"
      end
    '

I think the answer is no - this would affect any Rails app with default settings that uses ActiveStorage. The "Preconditions" recap at the bottom here has all the appropriate caveats: https://ethiack.com/info-hub/research/kindarails2shell-how-a...

I am not sure, but my read on the original disclosure is no. libvips itself has a variant processor for matlab v5 files, which the exploit took advantage of.