Rails before 1.2.4, as used for Ruby on Rails, allows remote attackers and ActiveResource servers to determine the existence of arbitrary files and read arbitrary XML files via the Hash.from_xml (Hash#from_xml) method, which uses XmlSimple (XML::Simple) unsafely, as demonstrated by reading passwords from the Pidgin (Gaim) .purple/accounts.xml file.
http://www.vupen.com/english/advisories/2007/4238
http://www.vupen.com/english/advisories/2007/3508
http://www.us-cert.gov/cas/techalerts/TA07-352A.html
http://www.securityfocus.com/bid/26096
http://weblog.rubyonrails.org/2007/10/5/rails-1-2-4-maintenance-release
http://security.gentoo.org/glsa/glsa-200711-17.xml
http://secunia.com/advisories/28136
http://secunia.com/advisories/27657
http://lists.apple.com/archives/security-announce/2007/Dec/msg00002.html
http://docs.info.apple.com/article.html?artnum=307179