A few days ago, ruby 1.9.3p327 was released to handle a possible DoS issue.
Is there a way to upgrade ruby version in Heroku? right now I have ruby 1.9.3p286 (2012-10-12 revision 37165) [x86_64-linux]
when I put ruby "1.9.3" in my gemfile
Update
Heroku updated the ruby version on cedar to p327
You can't specify a patch number in your Gemfile, you can only set the version number. Heroku will manage the patch levels so you will need to wait until they upgrade it.
See