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Web Apps with Tiger: Security and MySQL

by Kevin Hemenway
08/30/2005
Your Life in Web Apps

In our "Getting Started" part of this series, I was a little too fast and a little too slow. Like a confused lover, I went too fast because I didn't want to bore you with protracted explanations and foreplay about topics we may both already know. On the other hand, it was a little too slow because we really didn't accomplish much besides enabling PHP and verifying it worked.

In this, our second part of "Web Apps with Tiger", we'll be focusing on protection. We'll replace the default PHP configuration with a more secure version, and explain some of the differences. Finally, we'll install MySQL, our database server, and run through its own security tweaks. In the end, we'll be satisfied, but certainly desiring more.

Now Is the Time for Caring

In the last article, we finished with an index.php file containing the contents below. When saved into /Library/WebServer/Documents/ and accessed from http://127.0.0.1/, we saw a boatload, nay, multiple boatloads, of configuration options relating to PHP. Load up that file again, as we'll be exploring some of what we see.

<?php phpinfo(); ?>

The first line of interest is Configure Command. This contains the exact configure command (duh...) Apple used to build the PHP module for Tiger. Since most additional features and extensions of PHP are enabled during this configure process, we can get a good idea at what "extras" we're getting by examining this line: Apple has seen fit to enable command-line usage, XML parsing, EXIF information for images, FTP support, and so on. For those in the know, you'll be particularly distraught to see no image creation or modification capabilities, such as GD. This is the same as it has always been, and I'll address it in the future as necessary.

Next is the Configure File (php.ini) Path, which alludes to a file named /etc/php.ini where we could fiddle with our PHP settings. This file doesn't actually exist, meaning that PHP starts up with all its default configuration. This default config is represented by what we do have: /etc/php.ini-default. We could, if we wanted, rename that to php.ini and make changes there. Instead, however, we'll be using an entirely different source.

Switching to a More Secure php.ini

Open the /etc/php.ini-default in your favorite editor and read the first few lines:

; This is the default settings file for new PHP installations.
; By default, PHP installs itself with a configuration suitable
; for development purposes, and *NOT* for production purposes.
; For several security-oriented considerations that should be taken
; before going online with your site, please consult php.ini-recommended
; and http://php.net/manual/en/security.php.

Even with this admonishment, very few people actually switch to something stronger: inevitably, they code, they code, they code, they release, phew! All done, time for vacation, forget all about security. Before we get serious with any sort of PHP application, we're going to switch to the "recommended" version of the php.ini. It won't be an oversight.

Annoyingly enough, this configuration doesn't exist on our hard drive, and is quite difficult to find just layin' around in a Google result. Instead, we'll have to download a brand new source installation of PHP, just to grab the one file we're interested in: php.ini-recommended. Extract the archive and move this file into its proper place:

morbus@:~/Desktop > tar xzf php-4.4.0.tar.gz
morbus@:~/Desktop > sudo mv php-4.4.0/php.ini-recommended /etc/php.ini
morbus@:~/Desktop > ls -l /etc/php.ini
 -rw-r--r--   1 morbus  staff  39480 Apr 28 09:14 /etc/php.ini

With that done, delete the archive and restart Apache:

morbus@:~/Desktop > rm -rf php-4.4.0*
morbus@:~/Desktop > sudo apachectl restart
 /usr/sbin/apachectl restart: httpd restarted

Reload the index.php page; unless you've been incredibly astute or have been watching one single variable, you probably won't notice anything has changed. For an explanation of what this process did, along with reasons why, open the /etc/php.ini in an editor and read through the intro regarding register_globals, display_errors, log_errors, etc. Of chief and immediate interest is that PHP errors will no longer be sent to the browser: you'll have to check your error_log whenever PHP code doesn't seem to work correctly. I'll throw in another tailDash recommendation: it allows you to simply F12 your way to log viewing.

While we're in here, we may as well make two other small changes that I prefer, but which are certainly not required. The first relates to the memory_limit setting, which measures how much memory a PHP script can consume. The default is 8M--I usually set this anywhere from 16M to 64M, depending on the types of scripts I plan to be running, for how long, and the capabilities of the hardware itself. 24M is a decent enough value to start with. Generally speaking, if a single script is exceeding a 24M-memory limit, something is usually amiss.

I also like to turn Off the allow_url_fopen feature, though this is more cautious paranoia than any tried-and-true trick. This setting allows the PHP fopen function to load remote documents stored on other web servers, and has been implicated in a number of break-ins with poorly designed applications. Turn it Off for now, and if you ever need to use it in the future, you'll probably be smart enough to make a more informed decision.

If you made either of the above changes, restart Apache again.

Your Life in Web Apps

Essential Reading

Your Life in Web Apps
By Giles Turnbull

Have you dreamed of a simpler life where web apps and a browser meet all of your computing needs? All you need is a network connection. In this PDF Giles Turnbull introduces you to a day of web apps-only, then he surveys the best and most innovative web apps from the current crop available right now. He also addresses practicality, security issues, and backup strategies for living the web app life. Is it really possible? This PDF will help you decide.


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