lib/minimagick.rb in the MiniMagick Gem 1.3.1 for Ruby allows remote attackers to execute arbitrary commands via shell metacharacters in a URL.
In lib/minimagick/image.rb in MiniMagick before 4.9.4, a fetched remote image filename could cause remote command execution because Image.open input is directly passed to Kernel#open, which accepts a | character followed by a command.