The cross-site scripting (XSS) prevention feature in Ruby on Rails 2.x before 2.3.12, 3.0.x before 3.0.8, and 3.1.x before 3.1.0.rc2 does not properly handle mutation of safe buffers, which makes it easier for remote attackers to conduct XSS attacks via crafted strings to an application that uses a problematic string method, as demonstrated by the sub method.

The session fixation protection mechanism in cgi_process.rb in Rails 1.2.4, as used in Ruby on Rails, removes the :cookie_only attribute from the DEFAULT_SESSION_OPTIONS constant, which effectively causes cookie_only to be applied only to the first instantiation of CgiRequest, which allows remote attackers to conduct session fixation attacks. NOTE: this is due to an incomplete fix for CVE-2007-5380.