According to an advisory from the Apache-backed project, some of the vulnerabilities can be triggered remotely under certain circumstances. "This is a major stability and security enhancement of the 5.X branch, and all users are strongly encouraged to upgrade to it as soon as possible," the group warned.
Secunia rates the update as "moderately critical" and stressed that there are unspecified overflows that can be exploited to cause a stack overflow in the session extension. The "safe_mode" and "open_basedir" protection mechanisms in PHP can also be bypassed via the session extension.
Stack overflows also exist in the "zip", "imap", and "sqlite" extensions while a boundary error within the stream filters can be exploited to cause a buffer overflow.
The big security upgrades comes ahead of plans by PHP security guru Stefan Esser to launch a Month of PHP Bugs project in March 2007.