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.