https://groups.google.com/forum/#!topic/rubyonrails-security/61bkgvnSGTQ/discussion
There are multiple weaknesses in the parameter parsing code for Ruby
on Rails which allows attackers to bypass authentication systems,
inject arbitrary SQL, inject and execute arbitrary code, or perform a
DoS attack on a Rails application. This vulnerability has been
assigned the CVE identifier CVE-2013-0156.
Versions Affected: ALL versions
Not affected: NONE
Fixed Versions: 3.2.11, 3.1.10, 3.0.19, 2.3.15
Impact
The parameter parsing code of Ruby on Rails allows applications to
automatically cast values from strings to certain data types.
Unfortunately the type casting code supported certain conversions
which were not suitable for performing on user-provided data including
creating Symbols and parsing YAML. These unsuitable conversions can
be used by an attacker to compromise a Rails application.
Due to the critical nature of this vulnerability, and the fact that
portions of it have been disclosed publicly, all users running an
affected release should either upgrade or use one of the work arounds
immediately.
–
David N. Welton