Guidelines on Securing Public Web Servers

In addition, use the Web server s operating system to limit files accessed by the Web service 

processes.  These processes should have read only access to those files necessary to perform 

the service and should have no access to other files, such as server log files.  Use Web server 

host operating system access controls to enforce the following [CERT01]: 

Web service process(es) is (are) configured to run as a user with a strictly limited set 

of privileges (i.e., not running as root, Administrator, or equivalent). 

Web content files can be read but not written by Web service process(es).  

Web service process(es) cannot write the directories where public Web content is 

stored.  

Only process(es) authorized for Web server administration can write Web content 

files.  

The Web server application can write Web server log files, but log files cannot be 

read by the Web server application.  Only root/system/administrative level processes 

can read Web server log files.  

Temporary files created by the Web server application, such as those that might be 

generated in the creation of dynamic Web pages, are restricted to a specified and 

appropriately protected subdirectory.  

Access to any temporary files created by Web server application is limited to the Web 

service process(es) that created these files.  

It is also necessary to ensure that the Web server application cannot save files outside the 

specified file structure dedicated to public Web content.  This may be a configuration choice in 

the server software or it may be a choice in how the server process is controlled by the 

operating system.  Ensure that such directories and files (outside the specified directory tree) 

cannot be served, even if users know the names or the Uniform Resource Locator (URLs) of 

those files. 

To mitigate the effects of certain types of DoS attacks, configure the Web server to limit the 

amount of operating system resources it can consume.  Some examples would include the 

following: 

Install Web content on a different hard drive or logical partition from the operating 

system and Web application. 

If uploads are allowed to the Web server, place a limit on the amount of hard drive 

space that is dedicated for this purpose. 

If uploads are allowed to the Web server, these files should not be readable by the 

Web server.  They should only be readable by the Web server after some automated 

or manual review process.  This prevents the Web server from being used to traffic 

pirated software, attack tools, pornography, etc.   

Ensure that log files are stored in a location that is sized appropriately. 

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