Question

How can PHP cause memory leaks, buffer overflows, stack overflows and any other errors of such kind? Can PHP even cause such errors?

Answer 1

By causing some kinda infinite recursion, you can cause a PHP crash.

For example, a file that recursively requires itself should cause a stack overflow:

require __FILE__;  

Or a recursion in the magic __sleep() method that is supposed to unserialize an object, but calls serialize() instead:

class sleepCrasher
{
    public function __sleep()
    {
        serialize($this);
    }
}

serialize(new sleepCrasher());

Or a class destructor that creates new instances:

class destructorCrasher
{
    public function __destruct()
    {
        new destructorCrasher();
    }
}

// Calling __destruct() manually is just for the sake of example, 
// In real scenarios, PHP's garbage collector will crash PHP for you.
(new destructorCrasher())->__destruct();

As well as a recursive __toString():

class toStringCrasher
{
    public function __tostring()
    {
        return strval($this);
    }
}

strval(new toStringCrasher());

There are other recursion scenarios that PHP is protected against. For example, calling a recursive function without an exit condition or a recursive self-yielding generator. These ones do not cause a crash, but a Allowed memory size of ... fatal error.

For more examples, you might want to see:

• PHP Crashers
• Top 10 ways to crash PHP