Secunia has released an advisory for Mandriva users to update their PHP installations to the new packages provided:

Mandriva has issued an update for php. This fixes some vulnerabilities, where one has an unknown impact and the others can be exploited by malicious users to bypass certain security restrictions and potentially by malicious people to compromise a vulnerable system.

Several RPMs are available from Mandriva to update your installation. Check out the original security advisory from Mandriva for more information and which packages you'll need to get.