command_wrap.rb in the command_wrap Gem for Ruby allows remote attackers to execute arbitrary commands via shell metacharacters in a URL or filename.
http://www.openwall.com/lists/oss-security/2013/03/19/9
http://seclists.org/fulldisclosure/2013/Mar/175
http://packetstormsecurity.com/files/120847/Ruby-Gem-Command-Wrap-Command-Execution.html