Guidelines on Securing Public Web Servers

Install or enable only necessary services.  

Install Web content on a dedicated hard drive or logical partition.   

Limit uploads to directories that are not readable by the Web server. 

Define a single directory for all external scripts or programs executed as part of Web 

content. 

Disable the use of hard or symbolic links. 

Define a complete Web content access matrix that identifies which folders and files 

within the Web server document directory are restricted and which are accessible (and 

by whom).  

Disable directory listings. 

Use user authentication, digital signatures, and other cryptographic mechanisms as 

appropriate.   

Use host based intrusion detection systems and/or file integrity checkers to detect 

intrusions and verify Web content.   

Organizations should use active content after carefully balancing the benefits gained 

against the associated risks.    

In the beginning, most WWW sites presented static information residing on the server, 

typically in the form of text based documents.  Soon thereafter, interactive elements were 

introduced to offer users new ways to interact with a Web site.  Unfortunately, these same 

interactive elements introduced new Web related vulnerabilities, since they involve moving 

code from a Web server to a client for execution.  Different active content technologies have 

different associated vulnerabilities, which must be weighed against their benefits.

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Organizations must use authentication and cryptographic technologies as appropriate to 

protect certain types of sensitive data.   

Public Web servers often support a range of technologies for identifying and authenticating 

users with differing privileges for accessing information.  Some of these technologies are 

based on cryptographic functions that can provide an encrypted channel between a Web 

browser client and a Web server that supports encryption.  Web servers may be configured to 

use different cryptographic algorithms, providing varying levels of security and performance. 

Without proper user authentication in place, organizations cannot selectively restrict access to 

specific information.  All information that resides on a public Web server is then accessible by 

anyone with access to the server.  In addition, without some process to authenticate the server, 

users of the public Web server will not be able to determine if the server is the  authentic  

Web server or a counterfeit version operated by a malicious entity. 

3

 See NIST Special Publication 800 28, 

Guidelines for Active Content and Mobile Code

(

http://csrc.nist.gov/publications/

) for more extended discussion and advice on the policy and technical issues of 

active content. 

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