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This is an excellent approach and one I often recommend. It's very clear, plus it doesn't depend on any variables. Hard coded strings are very safe and obvious.

In contrast, look at how unclear the other suggestions are in comparison.


One security principle to which I adhere (or try to) is to never try to correct invalid data. When you do, you create an opportunity for you to make a mistake that yields a security vulnerability. For example, here is an approach I have observed quite frequently:


Can you think of a way around this?


That's not true. The way include works is the file (or resource) you reference is treated just like any other PHP file. If there are no PHP blocks, it's treated as raw output.


Roja++


What he said isn't correct, because going above root doesn't fail. Maybe it does on Windows or something, but the parent directory of root is root.


I have no idea what you think you've proven, but try this:

/home/blah/public_html/../../../../../../../../../../etc/passwd

If you're on Windows, that won't work either, but maybe you get the idea.


Includes are treated just like any other PHP file. The only code that is executed is within PHP blocks. Everything else is just raw output.

So, if you're referring to his example of index.php, you're right. If this is the case, just be careful to qualify your statements. :-)

Hope that helps.

Actually, going above the root does fail. If you use the correct number of parents, you can explore to directories next to the directory in question.


My code sample shows that you can use parent dirs (../), which previous posts claimed you couldn't do ("You can't access anything but the directory"). It allows you to go above, sideways, and below. By using the absolute value from the root, you can go all the way up, and all the way down.

From my reading, we actually agree, but your phrasing seems to indicate that you didn't quite understand what I meant.

On what platform? I'm not aware of any platform that has this behavior.

Yes I can. And yes normally I wouldn't correect the data, only detect and reject. (Ie check if filename = basename or reject) slightly strong versions can check for forward/backward slashes under a somewhat long set of encodings and reject in those as well.


Not true in this case. The OP was concatenating ".php" onto the user-provided name. That's what I mean by a PHP file, not a parsed file, but I can see the opportunity for confusion. Even if they asked for /etc/passwd it would end up being /etc/passwd.php

Same here... The only exception I'm aware of is if you've mada chroot/jail.

I see now. Thanks.

An attacker can get around the .php concatenation on many platforms by using a NUL byte. For example:

http://example.org/test.php?p=../../../ ... /passwd%00

Try it - you might be surprised by the results.

Yup I've seen that too...

All these little exceptions is why I don't do user-provided includes. If I had to, I'd use the basename function, coupled with a regexp ([-A-Za-z0-9_]), with forced ending (.php or .inc depending on your preference, etc‚). The null-byte, full stops. and slashes wouldn't survive that.

As always, state what you'll accept, not what you'll reject. Its too easy to miss something if you only list the bad stuff.

Oh, i see the security holes now. But no - I keep my server as clean as possible.

http://www.php.net/realpath can come in quite handy

how's this when you are simply including basic pages?

also, I was wondering if there is any way around I have tried to ../ my way out of it, but it seems secure.

Well the null byte can stop the .php. I'm not sure if an attacker could get a series of ^H control code in to delete the prefix, but that might be possible via some encoding or another.

I'm completely inexperienced regarding security issues and still very new to using PHP. From what I've read so far, am I in better shape for using an array of approved includes? This is the method I read about and it is the one I am using. Should I be using a different method? (I am using a testbed server at home for the time being.)

Yes, an explicit list of approved includes is a much more secure starting point. Its still possible to "mess it up" but its generally much safer.

Bit of forum Necromancy here, I sometimes use the following:


on my front controller(s)

and that has to be the best way I've ever seen.