Note: This blog post is from 2013. Some content may be outdated--though not necessarily. Same with links and subsequent comments from myself or others. Corrections are welcome, in the comments. And I may revise the content as necessary.

As an update since I first wrote this, it turns out this issue may or may not affect you depending on a couple of variables, which I will discuss, with a prefix of "update:" below. But don't dismiss this thinking you are not affected. I would propose that still far more CF servers may be exposed than not, as I will explain.

The CF Admin has (for several releases) offered an option called, "Use UUID for cftoken" (in the "Settings" section), and it's been intended as a security measure. Its purpose is to cause CF to use a UUID value (a long, complex string of numbers and letters) for the CFTOKEN cookie (and session variable) that CF generates, versus what used to be a simple, 8-digit value. This cookie, along with the simpler and incrementing CFID, is used to connect users to the session and/or client scope values created for that user in CF code.

Some may be surprised to learn, though, that while this setting DOES cause CF to *create* such UUID-formatted CFTOKEN values for requests that do not already present a CFTOKEN cookie, it does NOT necessarily cause CF to block any continued use of such simple, 8-digit cftoken cookies.

In other words, browsers which had visited your site before you turned on "use uuid for cftoken" would still send the 8 character cftoken they already had, not a uuid, and that could be accepted as valid by CF, even with that setting on, under certain conditions. (And the user will not be sent any new cftoken cookie in a UUID format, in CF's response, in those conditions.)

There's good and bad news related to this fact, which I will elaborate on below.

Update: Since writing this entry, I learned of a couple of factors that influence if and when this is a problem.

1. It turns out that if you are using CF10, or CF9 or 8 with the "session fixation" hotfix (APSB11-04), then the problem only happens until you restart CF. The Admin does not currently warn you of this, so beware that you will have the exposure below until you do restart. (If you have added one of the later security hotfixes or cumulative hotfixes that came out since then, then you have gotten the fix.) This fix causes CF to create a new UUID-based CFTOKEN, if you turn on this feature at least (and after a restart) when a browser presents a previously created 8-digit cftoken.
2. On the other hand, even if you are running CF 10, or running 8 or 9 and HAVE applied that hotfix, note that if you TURN OFF that fixation protection (by adding the -Dcoldfusion.session.protectfixation=false value to your jvm.config, as discussed in that technote), then you are back to the state that I discuss below.
3. And of course, if you are on CF 8 or 9 and have NOT yet applied that APSB11-04 hotfix (or a later cumulative one that includes it), then you are indeed still vulnerable.

So that leaves still many people who could be affected by this. Even if it seems you may not be, you may want to continue reading this entry to understand what the issue is about, for you and others who may be impacted by it.

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