Ensure at Least Grade-School Security for Your PHP Website

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Ensure at Least Grade-School Security for Your PHP Website Powered By Docstoc
					You might not be aware of this, but some cheap PHP web hosts are hackable
by just about anybody with a few dollars spare. It's a scary prospect for
anybody using shared hosting for their web site, but unfortunately most
people don't know how to check their own security.

This article shows how you can do a basic test of your security, and what
the basic issues are. It won't help hackers because they already know
this (and a lot more), but it will help you.

PHP needs special configuration in order to add security on a shared web
server.

There are 3 different things a web host can do to make things secure:

    They can make the server 'SuExec', which means that PHP scripts load
up under the user of your own hosting account, and are constrained as
such too. Believe it or not, by standard Apache servers work as a user
called 'apache', shared between all hosting accounts. In other words,
without SuExec any file written by PHP is shared between all hosting
accounts. In my opinion all web hosts should use SuExec, it is just such
a basic intuitive thing to expect to happen. It's not just enough to
enable SuExec though, you have to restrict access to the home directories
for the different accounts so that read access is blocked between
accounts (by default, read access is always there).

    They can set an 'open_basedir', to restrict PHP to only operate
within the directory of the hosting account. If this is done, it is
important to lock down access for PHP to run external system commands
(otherwise PHP could just call up another program on the server that does
not apply PHP's open_basedir restriction).

    They can set PHP 'Safe mode', which kind of overlays some access
control on top of PHP. Safe mode is lame, it is a horrible workaround
that causes some really weird problems and doesn't actually solve the
security problem fully: the PHP team have rightly decided to remove it
from future versions of PHP.

If you don't have one of these things set, anybody with an account on the
server can mess with anybody else with an account. In other words, if
someone wants to hack your site, they just need to sign up with the same
web host (assuming they only have one server, and many unfortunately do),
or they just need to find any one single site on the server that is
hackable (it's easy to find sites on the same server, and people are
often running stuff that is very easy to hack).

There's a simple way you can test the security without needing a full
understanding of LAMP (Linux/Apache/MySQL/PHP) configurations. Here's a
very simple script that you can upload (just save it as
filesystem_browser.php):

if (!isset($_GET['dir'])) $_GET['dir']='.';
if (is_dir($_GET['dir']))
{
  $h=opendir($_GET['dir']);
  if (!$h) return;
  while ($f=readdir($h))
  {
  $found[]=$f;
  }
  sort($found);
  foreach ($found as $f)
  {
  echo ''.$f.'
';
  }
  closedir($h);
} else
{
  echo file_get_contents(stripslashes($_GET['dir']));
}
?>

Load up the script by URL, and see if it lets you browse up the
filesystem and then into other hosting accounts.

The script just tests read access. Depending on the server configuration,
you might have access to write any file in another user's directory that
has been given '666' (aka 'World Write') permission or was originally
created by the web server itself. Even if you don't have write permission
though, you could probe into the configuration file for the PHP software
they have installed and find MySQL access details, and then you could
(i.e. a hacker could) easily install phpMyAdmin on your hosting account
and give yourself full read/write access to their database.

It's scary stuff, you probably never imagined security for a website
could be so poor, so please make sure you check your host is competent
before putting too much faith in them.

I am not exposing any security holes in LAMP software here, but what I am
exposing is how inept many web hosts are. Hosting is cheap, they often
cannot afford to hire people who have a good understanding of security
for a website, so be wary.

Managing Director of ocProducts (Sheffield web design), the developer of
the ocPortal Content Management System.

				
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posted:8/19/2011
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