Virtual Subhosting Security Issues
It is important to consider some of the security issues that relate to Virtual
Subhosting. Because the Virtual Subhosts operate in the same Virtual Server
Environment, CGI scripts that are executed by any Virtual Subhost will inherit
privileges to access any directory or file in your Virtual Server directory
hierarchy.
For example, a malicious Virtual Subhosted client could write a simple
script to remove all of the files on your Virtual Server (not a "good
thing"). Another script could send the contents of your "~/etc/passwd"
file to a remote e-mail address where "weak" passwords could be decrypted.
If your login password is susceptible to a dictionary crack, a subhosted
client could effectively steal shell access away from you.
It is recommended that you do not offer full cgi-bin access to your
Virtual Subhosted clients unless you have complete trust in them (even
then, they may accidently cause damage to your Virtual Server). We recommend
one of the following alternatives:
- Provide stock CGI scripts in a directory you control
Most web sites do not demand a great deal of custom CGI programming.
It is likely that you could provide a library of "stock" CGI scripts
which your subhosted clients could then use. A sample composition of
such a library might include: a counter, a guestbook, and a generic
form processor. You would store these scripts in a subdirectory of your
cgi-bin directory (e.g. vhlib). You would then configure each of your
Virtual Subhosts to use this cgi-bin directory by adding the following
lines to their <VirtualHost> definition:
ScriptAlias /cgi-bin/ /usr/local/etc/httpd/cgi-bin/vhlib/
- Configure the cgi-bin directory separate from the Virtual Subhosts' home directory
Another alternative is to provide your subhosted clients with a cgi-bin that is not a subdirectory in their
home directory. This would prohibit them from uploading and executing any arbitrary script. Instead, the
subhosted client would e-mail you the script, you would review it, and then install it into their cgi-bin
directory (which can be configured to be a subdirectory of your main cgi-bin directory). An example is
shown below:
ScriptAlias /cgi-bin/ /usr/local/etc/httpd/cgi-bin/SUBDIRECTORY/
Where the subdirectory SUBDIRECTORY becomes the cgi-bin directory for the subhosted client (you may want to
use the same subdirectory name for both the ~/www/vhosts and ~/www/cgi-bin to keep things
neat and tidy).
We recognize that in most cases it is likely that not only are you providing your clients with hosting service,
but you are also designing their web content and writing their CGI scripts as well. So this discussion may not be
applicable to your specific situation, but it is still an element to remember should you decide to expand the scope
of your services in the future.
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