Different programming environments enforce security to different degrees, with different defaults. I'll here post some of the many criticisms that have been aimed at PHP over the years:

Andrew van der Stock writes:

--------------

For some time, I’ve been worried about the direction of PHP. As many of you know, I helped write XMB Forum and now help write UltimaBB. XMB in particular is an old code base, and UltimaBB, a descendant from XMB. I’ve done a lot to protect that code base from attack, and luckily, we’ve been missed despite some doozy and silly security issues. After writing PHP forum software for three years now, I’ve come to the conclusion that it is basically impossible for normal programmers to write secure PHP code. It takes far too much effort.

PHP needs a proper security architecture, and support for newbie programmers. PHP’s raison d’etre is that it is simple to pick up and make it do something useful. There needs to be a major push by the PHP Development team to take this advantage, and make it safe for the likely level of programmers – newbies. Newbies have zero chance of writing secure software unless their language is safe.

Think about Logo for a minute. Logo can do some interesting things, but it is not a commercially useful language because it cannot do much. But it is an excellent teaching language. PHP is like Logo – it’s a simple and easy way to get into serious web development. It is possible to write large applications in PHP, so it is useful at that level. But it is inherently unsafe as it can do far, far more than Logo.

There are so many ways to break PHP that it is impossible for even experienced security professionals like me to code in it securely all the time. There are nearly 4000 function calls, and many of them have unintended consequences or have been inappropriately extended by something else.

http://www.greebo.net/2006/01/04/php-insecurity-failure-of-l...

---------------

Tim Bray put together a collection of links regarding criticism of PHP:

http://www.tbray.org/ongoing/When/200x/2006/02/17/PHP

On that page, there is this from Dominic Mitchell:

"I’m in 100% agreement with you about the whole PHP thing. Every time I’ve looked at PHP, I’ve been unable to find out how they use placeholders in code that talks to the database. Yes, every database adaptor provides a quote function, but nobody uses it (consistently). And people wonder why PHP code is always full of security holes. It’s a real shame, as I can see that there’s a lot to like in PHP. But it really needs to clean its act up to appeal to people coming from other programming languages, instead of just people coming from dreamweaver. I actually heard David Heinemeier Hansson (sp?) talking about rails the other day. One of the key points he made is that it should be easy to do the right thing. That’s why Rails hits a sweet spot for me. But when you look at PHP, yes, it’s easy to code, but it’s not easy to do the right thing. That’s where it falls down."

The point that Hansson makes about Ruby is worth thinking about in the context of PHP security. Does PHP make it easy to write secure code? Does it help programmers do the right thing? The defaults in PHP, and the underlying assumptions of PHP, all tend in what direction?

Of those links, Jonas Maurus's post is also well worth reading:

http://maurus.net/resources/programming-languages/php/

Aristotle Pagaltzis sums up the underlying problem:

"All of these flaws are interconnected; the morass is simply the result of the language being a templating system that grew too big for its breeches. I don’t believe the problems can be corrected in any sensible fashion; PHP will always be a templating system, however much it may be straining against its clothes.
And let me tell you, it’s still a great templating system! If all you need is to write a web app that consists of two pages, running four queries over a five-table database, there is nothing that will get you up and running faster."

http://plasmasturm.org/log/393/