Atomic builds of mysql are not vulnerable to this exploit. We just went through and tested just about everything we did as far back as 5.0.90 without success.

Fedora 17, native 5.5.23 (not atomic) *is* vulnerable, as are just about every version on debian or ubuntu. If you are using a vulnerable version and cannot upgrade to the atomic build, this is about as critical a vulnerability as it gets. Its exploitable by the most unsophisticated of attackers, and very fast.

Also see this Red Hat Bugzilla report: http://bugzilla.redhat.com/show_bug.cgi?id=814605

According to http://bugzilla.redhat.com/show_bug.cgi?id=814605#c19 EL4-6 are not vulnerable, but x86_64 SSE4 builds, like the Fedora one, are.

as this is a compiler introduced vulnerability, I would expect to see more attacks of this nature pop up in the future.