The to_s method in actionpack/lib/action_dispatch/middleware/remote_ip.rb in Ruby on Rails 3.0.5 does not validate the X-Forwarded-For header in requests from IP addresses on a Class C network, which might allow remote attackers to inject arbitrary text into log files or bypass intended address parsing via a crafted header.
http://www.openwall.com/lists/oss-security/2011/08/22/5
http://www.openwall.com/lists/oss-security/2011/08/22/13
http://www.openwall.com/lists/oss-security/2011/08/20/1
http://www.openwall.com/lists/oss-security/2011/08/19/11
http://www.openwall.com/lists/oss-security/2011/08/17/1
http://archives.neohapsis.com/archives/fulldisclosure/2011-02/0337.html