"We're still hard at work on Rails 1.2, which features all the new dandy REST stuff and more, but a serious security concern has come to our attention that needed to be addressed sooner than the release of 1.2 would allow. So here's Rails 1.1.5!
This is a MANDATORY upgrade for anyone not running on a very recent edge (which isn't affected by this). If you have a public Rails site, you MUST upgrade to Rails 1.1.5. The security issue is severe and you do not want to be caught unpatched.
The issue is in fact of such a criticality that we're not going to dig into the specifics. No need to arm would-be assalients."