Virtual Subhosting Security Issues

It is important to consider some of the security issues that relate to Virtual Subhosting. 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.

Because the Virtual Subhosts operate in the same Virtual Private Server Environment, CGI scripts that are executed by any Virtual Subhost will inherit privileges to access any directory or file in your Virtual Private Server directory hierarchy. For example, a malicious Virtual Subhosted client could write a simple script to remove all of the files on your Virtual Private Server. 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 Private Server). We recommend one of the following alternatives:

1. 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 pre-made 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. 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/sub-lib/

2. Configure the cgi-bin directory apart from the Virtual Subhost 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/

   In this case, SUBDIRECTORY becomes the cgi-bin directory for a specific 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).