Earlier quoted context omitted.
This vulnerability went from disclosure to exploit extremely quickly. The CVE was published on the 8th. I can't speak for them, but in the process of trying to update, we ran in to some issues with therubyracer (a core component of the Rails asset pipeline) and libv8 (the library that therubyracer uses to embed the V8 engine). It was extraordinarily bad timing, and it slowed down our update process by almost a day wh…
You cannot leave your site open to a pre-auth remote code execution vulnerability while you wait for fixes to the asset pipeline or to any other component of Rails. I don't know that that's what you're saying you did but we need to be glacier-blue-ice-clear about this. Nobody gets to wait on bugs like this. You patch or workaround immediately or, most probably, you shut your app down.
EDIT: I guess that qualifies as a mitigation strategy, but when I said that, I was talking more along the lines of the patches, or like another person I know, even more dramatic steps like forking Rails. There are regressions in the 3.2.x updates since 3.2.9 that affect some sites.
Bottom line is that there was a lot of bad timing here that sucked up a lot of time in securing a Rails site.