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Filesystem Security> <Case 4: PHP parser outside of web tree
[edit] Last updated: Fri, 22 Jul 2011

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Installed as an Apache module

When PHP is used as an Apache module it inherits Apache's user permissions (typically those of the "nobody" user). This has several impacts on security and authorization. For example, if you are using PHP to access a database, unless that database has built-in access control, you will have to make the database accessible to the "nobody" user. This means a malicious script could access and modify the database, even without a username and password. It's entirely possible that a web spider could stumble across a database administrator's web page, and drop all of your databases. You can protect against this with Apache authorization, or you can design your own access model using LDAP, .htaccess files, etc. and include that code as part of your PHP scripts.

Often, once security is established to the point where the PHP user (in this case, the apache user) has very little risk attached to it, it is discovered that PHP is now prevented from writing any files to user directories. Or perhaps it has been prevented from accessing or changing databases. It has equally been secured from writing good and bad files, or entering good and bad database transactions.

A frequent security mistake made at this point is to allow apache root permissions, or to escalate apache's abilities in some other way.

Escalating the Apache user's permissions to root is extremely dangerous and may compromise the entire system, so sudo'ing, chroot'ing, or otherwise running as root should not be considered by those who are not security professionals.

There are some simpler solutions. By using open_basedir you can control and restrict what directories are allowed to be used for PHP. You can also set up apache-only areas, to restrict all web based activity to non-user, or non-system, files.

add a note add a note User Contributed Notes Installed as an Apache module
Vikanich 14-Aug-2008 11:41
Big thanks to "daniel dot eckl at gmx dot de" but i have to change his config, because it doesn't work (may be wrong syntax).
I have add only this string to VirtualHost config and it works.
php_admin_value open_basedir  /www/site1/
Now all php scripts are locked in the directory.
Kibab 30-Sep-2005 01:56
I'm running Windows version of Apache with php as module. System is Windows XP Service Pack 2 on NTFS filesystem. To avoid potential security problems, I've set Apache to run under NT AUTHORITY\Network Service account, and there is only one directory, named Content, with Full Access for this account. Other directories are either not accessible at all or with readonly permissions (like %systemroot%)... So, even if Apache will be broken, nothing would happen to entire system, because that account doesn't have admin privilegies :)
tifkap 01-Mar-2004 11:21
There is a safe way to support a lot of users in a secure way, without having to use CGI, in a way which is probebly faster
than mod_php.

Use FastCGI, with the SuExecWrapper set to your suid wrapper. It means every user wil get his own program-group, with processes
which are being reused. If the numer of processes that is being
started on startup is 0, then the processgroup for a user will be generated when needed.

This means: The first page is slow, after that the Zend Engine  caching kicks in. When the load on the virtualhost reduces, the
processes wil die off, and extra processes for a user-process-group
will only be started when (again) needed.

Your apache will be a LOT! lichter, because it won't have to drag all
the php-memory overhead with it. This means static content is
faster, and the whole system uses less memory.
The PHP itself also won't need to drag along the apache overhead.

If for one reason or the other php craches, your apache will simple
start some new php-processes. If you want to upgrade/patch php,
you can simple create the new fastcgi binary, and after testing, you can simple update the system by copying it, and maybe doing a
'apachectl gracefull'

In short :  Sepparating distinct functions in different processes
                communicating useing IPC methodes can be very good
                for performance and security. The best example of this
                principle at work is Postfix, where every process runs
                chroot() under its own uid.
Georgee at CWC 30-Apr-2003 01:16
Additional CAUTION to anyone trying Pollux's solution:
It's kind a good. Probably works right. I think I'll give it a try myself. BUT...
its safe ONLY on the assumption that apache is 100% CLEAN. (codes and confs.) Any flaws on apache, almost ANYTHING could happen to ALL users -precisely, web users. (Because apache is a member of ALL -again, web user's- GID.) So, leeps's hint should be one of the important things.

There is nothing close to perfect. What I wrote is just one thing you'll have to keep in mind. So, consider carefully BEFORE you try this solution. (Well, this applies to any other solutions though...)
leeps 10-Mar-2003 01:59
@pollux: additionally, tell your users to set their file-permissions to
- r-- (group) for files
- --x (group) for directories.

this disables the webserver to browse user's directory. if you don't know the filename, you cannot open it, e.g. by running malicious php-code through one of the users scripts.
daniel dot eckl at gmx dot de 08-Aug-2002 11:16
There is a better solution than starting every virtual host in a seperate instance, which is wasting ressources.

You can set open_basedir dynamically for every virtual host you have, so every PHP script on a virtual host is jailed to its document root.

  DocumentRoot /www-home/
  <Location />
    php_admin_value open_basedir     \ "/www-home/"

If you set safe_mode on, then the script can only use binaries in given directories (make a special dir only with the binaries your customers may use).

Now no user of a virtual host can read/write/modify the data of another user on your machine.


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