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 accessable 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
abilitites 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.