tenderlove reports:

DoS Vulnerability in authenticate_or_request_with_http_digest

There is a DoS vulnerability in Action Pack digest authentication handling in Rails.
This vulnerability has been assigned the CVE identifier CVE-2012-3424.

Versions Affected:  3.x.
Not affected:       2.3.5 - 2.3.14
Fixed Versions:     3.0.16, 3.1.7, 3.2.7

Impact 
------ 

All users using Digest Authentication support in Rails should upgrade
immediately.  Impacted code uses any of the `with_http_digest` controller
helper methods.  For example:

    class MyController < ApplicationController
      def index
        authenticate_or_request_with_http_digest(REALM) do |uname|
          # ...
        end
      end
    end

Releases 
-------- 
The 3.0.16, 3.1.7 & 3.2.7 releases are available at the normal locations. 


Workarounds 
----------- 
There are no feasible workarounds for this issue. 


Patches 
------- 
To aid users who aren't able to upgrade immediately we have provided patches for the two supported release series.  They are in git-am format and consist of a single changeset. 

* 3-0-digest_auth_dos.patch - Patch for 3.0 series 
* 3-1-digest_auth_dos.patch - Patch for 3.1 series 
* 3-2-digest_auth_dos.patch - Patch for 3.2 series 

Please note that only the 3.1.x and 3.2.x series are supported at present.  Users of earlier unsupported releases are advised to upgrade as soon as possible as we cannot guarantee the continued availability of security fixes for unsupported releases.

Credits 
------- 
Thanks to Charlie Somerville for reporting this issue!

References:

http://weblog.rubyonrails.org/2012/7/26/ann-rails-3-2-7-has-been-released/
https://groups.google.com/forum/?fromgroups#!topic/rubyonrails-security/vxJjrc15qYM

diff --git a/actionpack/lib/action_controller/metal/http_authentication.rb b/actionpack/lib/action_controller/metal/http_authentication.rb
index 9f2f547..fe4ab65 100644
--- a/actionpack/lib/action_controller/metal/http_authentication.rb
+++ b/actionpack/lib/action_controller/metal/http_authentication.rb
@@ -227,9 +227,9 @@ module ActionController
       end
 
       def decode_credentials(header)
-        Hash[header.to_s.gsub(/^Digest\s+/,'').split(',').map do |pair|
+        HashWithIndifferentAccess[header.to_s.gsub(/^Digest\s+/,'').split(',').map do |pair|
           key, value = pair.split('=', 2)
-          [key.strip.to_sym, value.to_s.gsub(/^"|"$/,'').gsub(/'/, '')]
+          [key.strip, value.to_s.gsub(/^"|"$/,'').delete('\'')]
         end]
       end