According to wordpress.org:

2.2.3 is a security and bug-fix release for the 2.2 series. Since this is a security release, we suggest you upgrade immediately. Two of the fixes are high priority.

On our Trac you can see the bugs closed and the files changed for 2.2.3.

To get 2.2.3, please see our download page.

As always, upgrade instructions including an extended upgrade guide are available.

Thanks to Alexendar Concha, Aaron Newman, and xknown for identifying and helping us fix the security vulnerabilities.