Both CF 9.0 and 9.01 run on older JVMs (and therefore need this update). And are you on CF8? You're not left out: Adobe even has confirmed this update can be applied to CF 8 and 8.01, too!
Update 1: Since I wrote this blog entry in Oct 2011, Adobe has since come out with a new technote in Oct 2012 saying that you are now permitted to update to any version of Java 1.6 (for CF 8/9/10). Support for Java 1.7 is still not authorized.
Update 2: Since posting this note, I've realized I should document an important fact to be aware of if you DO update the JVM: after doing so, it may seem that changes you made to allow CFHTTP calls to SSL pages (or other tags in CFML that talk via SSL or TLS) may "seem to have been lost". The issue is that likely modified your current CF setup to import specific certificates for such sites, and those changes are "lost" on the JVM change in taht CF is now using a new JVM (and keystore), but these can be recovered. For more on that, see the next to last section below.
Old news, but not everyone knows
Someone mentioned today on a list that they'd seen news from Oracle of this important bug (and fix) for the JVM, which can cause someone to crash the JVM using a particular URL string. He also noted that while Oracle had released the fix some months ago, he lamented that "This issue doesn't seem to have gotten too much interest from Adobe."
I explained that in fact Adobe had addressed it, also some months ago.
Adobe offered a technote on the issue in March 2011.
In fact, they not only confirmed support for (and recommended updating to) the fixed JVM version, 1.6.0_24, but they even (for the first time in years) approved updating to this JVM version for CF 8 and 8.01. Since those ran on very old JVM releases, which had problems not fixed until JVM update 10, this was really good news.
But as his note conveys, word just had not gotten out as much as it could. Beside his thread on that list, I hope now that this blog entry will help reach more people.
More about the bug
If you want to know more about the bug from a CF perspective, check out this blog entry (from several months ago by David Stockton, of cfconsultant.com). He explains the problem/risk as well as shows how to cause the problem (to confirm when it's fixed), as well as some useful extra info on using FusionReactor to help diagnose it.
How to update the JVM for CF
So if you're now persuaded, you may wonder how you go about updating the JVM. You may fear it's like doing open-heart surgery. It's more like getting a mole removed. :-) It could go wrong, but will barely be noticeable if done right.
While it's not too hard to do, there are just a couple of potential gotchas: be sure to get the JDK not the JRE, and pay attention to the special path format that's needed when pointing to the JVM on Windows.
So if you're on CF and have not yet updated the JVM, seriously consider it.
Any potential compatibility problems with updating the JVM?
Since Adobe has given this update its blessing, we can assume that there should be no code compatibility issues. Of course, whenever you change the JVM you are changing the heart of the CFML engine, and there may well be changes between the version you're running and the version you upgrade to. Besides reading any technotes from Oracle/Sun, you should also keep an ear out in the community for any issues that people spot.
Indeed, since originally posting this entry, I realized that one potential issue is not so much due to any "change in behavior between JVM versions" but rather due simply to the fact that by changing what JVM CF is using, you're also inherently changing where it looks for certain information--which you may have updated yourself.
In brief, if you previously updated the java keystore (within CF) to enable you to do CFHTTP or similar tags to call an SSL page whose certificate CF/the JVM did not recognize, you will find these now "break" again, as if your changes were "list". What it is is that you (or someone at your site) did steps to import such needed new certificate into CF's keystore, but now on changing the JVM that CF uses, that will cause CF to instead use that new JVM's keystore. There are a couple of different solutions to this (import them again, export them from the old store and import again, point the new jvm at the old keystore, etc.), which I'll elaborate in the other blog entry.
What about updates beyond u24?This is an update since I posted the entry above. As you'll see in the comments below, some folks were kind enough to write in and point out that there have been JVM updates since u24.
I did realize that, and do appreciate their wanting to share the info. I'd not mentioned updates beyond 24 simply because I would not propose (myself) that anyone now update beyond the release for which Adobe has certified CF. (At least not until compelling reasons arise and substantial community testing suggests it may be safe, as happened with CF8 and the u10 update. Even then, you are risking being out of bounds for support by Adobe, so should make such a change with caution.)
The whole point of this entry was that u24 HAD in fact received Adobe's blessing, for CF 8 and 9, which was pretty compelling and seemed to have been missed by some when it happened earlier in the year.
Finally, since I wrote this note, again Adobe has now given their blessing to any update of JVM 1.6 for CF 8/9/10. More at this technote.