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Limitations of PHP5 - Upgrade / Downgrade
As we all know, nobody and nothing is perfect. Computer professionals have noticed vulnerability in PHP which can be exploited by those who are practicing Denial of Service (DoS) type attacks upon a system which is affected.

This limitation is caused by using in an improper manner the functions from libpng within the function gdPngReadData() in the source file ext/gd/libgd/gd_png.c of the extension GD, on the occasion of processing fragmented data. This can be exploited in order to force the execution entrance in an infinite loop by supplying a special file which is modified, to an application which uses the extension affected
Moreover, you have to know that this limitation was reported in the versions 4.4.7 and 5.2.2 and other versions can also be affected.
There is a solution to this limitation too, which can be found in some resources called Concurrent Versions System resources.
As far as PHP 5 limitations are concerned we can add that:
1. Protection mechanisms safe_mode and open_basedir can be avoided through the session management system.

2. Unspecified errors can be exploited in order to corrupt a memory area within the session.

3. Errors stack overflow type can be found within zip, imap and sqlite extensions.

4. A limitations check error can appear within the data flux processing and it can be exploited in order to force an error buffer overflow appear.

5. An error which is not specified and which is related to limitations overcome exists within the function str_replace().

But the good news is that regardless the limitation type there can be always found solutions.
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