The Slackware group has released an update to their PHP5 packages according to this new release on the Secunia site:

Slackware has issued an update for php5. This fixes some vulnerabilities, where one has an unknown impact and others can be exploited by malicious people to bypass certain security restrictions and cause a DoS (Denial of Service).

You can grab the updated packages via the original advisory and bring your installation up to date with the latest security fixes.