The PHP developers have released another update for both the 5.2 series and the 5.3 series. There is a critical issue that can cause PHP to hang and crash, causing your application to stall. They have provided a simple script you can run on your server (only from the command line, so this isn't for most people to test) to test for the vulnerability. I ran it in my local test environment and found it failed the test.

If your server is affected, you are strongly urged to upgrade to PHP 5.2.17 or 5.3.5.

Both XOOPS and ImpressCMS have released updates to address the recently disclosed security flaw. The National Vulnerability Database and SecurityFocus both reported details of a security flaw that affected both CMS platforms.
XOOPS has released version 2.0.18.2 RC and ImpressCMS has released version 1.0.2.RC
It is highly recommended you upgrade to the most recent version of either XOOPS or ImpressCMS to better secure your web site.