web technology – web server setup : chris uriarte meeting 4: advanced topics, continued: securing...

Web Technology – Web Server Setup : Chris Uriarte

Meeting 4: Advanced Topics, Continued: Securing the

Apache Server and Apache Performance Tuning

Rutgers University Internet Institute

Instructor: Chris Uriarte (CU520-03)


Today’s Session

• Protecting your Web server against attacks.

• Providing authenticated access to your Web site.

• Overview of SSL-enabled Web Servers

• Apache Performance Tuning

• Wrap-up and Evaluations


Levels of Web Server Security

• Protecting data supplied through client browsers.

• Protecting or restricting access to data stored on your Web server.

• Protecting the Web server software.

• Protecting the server that houses your Web server.


Common Attacks on Systems that Run Web Servers

• CGI exploits – Badly-written or buggy web applications (CGIs) programs

allow access to restricted resources or consume server resources.

• DoS (Denial of Service)– Software or operating system server exploits

• Packet sniffers– Hackers ‘sniff’ clear-text passwords

• Buffer overflows – Attacks that cause a piece of software to crash and possibly

give unprivileged users privileged access


Securing Your Web Server• Restrict access (by location or authentication) to file

systems and resources.– Password or IP authentication/authorization

• Disable server-side technologies if they are not required.– Disable CGI Access and Server Side Includes– Remove ExecCGI and Includes from the Options

directive of your httpd.conf

• Do not run your server as “root.” – The User directive in the httpd.conf should specify a user

other than root (e.g. nobody, www, etc.)


Securing Your Web Server, con’t.• Filter traffic with a firewall.

– Use of a network device that only allows access to particular resources on a network

• Use encryption technologies (ssh, ssl). • Monitor your logs for problems. • Secure the system that hosts your Web server: disable

ports and services not in use, install security patches, take preventative measures against popular exploits.– Websites like http://www.cert.org and

www.securityfocus.com have information on current exploits


Access by Authentication• Standard Authentication Modules – mod_auth,

mod_auth_anon, mod_auth_dbm, mod_auth_db, mod_digest

• Access in Apache can be defined by user or group:• For Basic Authentication: <Directory /home/iti1234/htdocs/restricted>

AuthType Basic AuthName “Restricted Access” AuthUserFile/usr/local/apache/passwd.fileAuthGroupFile /usr/local/apache/group.file require user1 group1 group2

</Directory>


Authentication, con’t.

• Authenticated access often setup through a .htaccess file in the directory you want to protect, but can be setup via httpd.conf.

• Passwords sent in the clear for basic authentication.


Basic Authentication: Line by Line

• You can keep authentication info in a <DIRECTORY> block in the httpd.conf or in an .htaccess file

• First, specify the AuthType, which is BasicAuthType Basic

• Next, Specify the text string that will be displayed when the username/pw box is presented to the user:AuthName “My Secret Webpages”

• Next, specify the path to a file that will contain the usernames and passwords of your users:AuthUserFile /home/apache/passwd.file

(best to keep this file out of the DocumentRoot)


Basic Authentication: con’t.

• Finally, add a require statement within a <Limit GET> block, which can limit the access to a specific username, or group. This can contain a list of groups, user names or the text “valid-user” to represent any valid user in the password file<Limit GET>

require valid-user

</Limit>


Basic Authentication: con’t

• The final block looks like this:<Directory /home/iti1234/htdocs/restricted>

AuthType Basic AuthName “My Secret Webpage” AuthUserFile/home/apache/passwd.file<Limit GET>

require valid-user <Limit GET>

</Directory>

• …which will prompt a user for a username/pw when any document under /home/iti1234/htdocs/restricted is requested.


Creating a Password File• htpasswd is a utility for generating encrypted

passwords and creating a password file• Part of apache distribution, located in : {SERVER ROOT}/bin/htpasswd

• Usage: htpasswd [-c] password-file username

• The –c flag creates a new password file. • Example, adds a user myname and creates a new password

file (type all on one line):/home/iti1234/bin/htpasswd -c /home/iti1234/apache/passwdfile username


Exercise: Password Protecting Your Website

• For this exercise, you will make the Website running on your workstation password restricted using a .htaccess file.

• In the directory container for your document root (/home/itiXXXX/apache/htdocs), in httpd.conf set the following: AllowOverride AuthConfig


Exercise, con’t:

• In /home/itiXXX/apache/htdocs, create a .htaccess file with the following contents: AuthUserFile /home/itiXXXX/apache/.htpasswd

AuthGroupFile /dev/null

AuthName “My Protected Site”

AuthType Basic

<Limit GET>

require valid-user

</Limit>


Exercise, con’t.

• Next, create a password file using htpasswd:htpasswd –c /home/itiXXXX/apache/.htpasswd guest

• Provide the password for the guest user when prompted.

• Access your website (http://iti.rutgers.edu:PORT/) and provide the username/password.


Restrict Access by Location Authorization

• As discussed in Meeting 2, you can restrict access to web resources by IP address, hostname, domain name and IP block by using a <DIRECTORY> block in the httpd.conf or an .htaccess file:<Directory /home/itiXX/htdocs/restricted> order deny,allow deny from all allow from 165.230.30.68 .rutgers.edu

</Directory>


Secure Socket Layer (SSL)

• Secure Socket Layer (SSL ) is a technology developed by Netscape that can be used to encrypt data sent between the client and a server.

• Mainly used for secure Web-based online transactions – stops network eavesdroppers from “listening” to your personal information, credit card numbers, etc.


How SSL Works• Client connects to the server. • Server sends back a certificate that contains the server’s

public key. • Server sends a digitally signed messaged encrypted

with its private key. The client decrypts the message using the server’s public key.

• Client uses server’s public key to encrypt a secret single-key.

• Secret single-key is used for encryption and decryption of all further communications between server and client.


Certificates and Certificate Authorities

• The “weak-link” in SSL transactions is initial communication between client and server. If connection is made to illegitimate server, the whole transaction is tainted.

• A certificate is used to pair a public-key with an owner’s identity.

• For this identity assertion to be trusted, the certificate must be signed by a Certificate Authority (CA) that independently verifies that identity of the owner of server’s public-key.

• Web browsers only recognize the validity of certain certificate authorities.


Getting a Signed Certificate• Web browsers will generate a warning when accessing

an SSL-enabled site that uses a certificate than hasn’t been signed by a recognized authority.

• Certificate Authorities: – Verisign http://www.verisign.com - Price for 40-Bit SSL

Certificate: $349…owned by NetworkSolutions– Thawte http://www.thawte.com - Price for 40-Bit SSL

Certificate: $125…now owned by Verisign

• Will need to provide a CSR (Certificate Signing Request) plus other documentation verifying that you are who you say you are and that you own the domain specified in the CSR.


Apache with SSL Options• Commercial Solutions

– StrongHold Server http://www.c2.net/products/sh2 Price: $995 (Includes certificate signed by Thawte)

– Raven SSL Module http://www.covalent.net/raven Price: $357

– Red Hat Secure Web Server (Linux Only) http://www.redhat.com Price: $150 (Part of Red Hat Professional Edition)

• Non-Commercial Solutions – Apache-SSL http://www.apache-ssl.org – Interface to OpenSSL (mod_ssl) http://www.modssl.org and

http://www.openssl.org


Other Non-Apache SSL Servers

• SSL capabilities built into other major web servers:– Microsoft IIS– Sun Java WebServer– O’Reilly Website


Apache SSL Configuration• SSL configuration for Apache-based web servers

differs greatly, depending on the SSL distribution you are using. Check the documentation for each distribution.

• Generally, SSL setup and configuration is easier with commercial distributions.

• Using a non-commercial SSL distribution (mod_ssl, Apache-SSL) usually requires you to install libraries on your system, re-compile Apache and add special configuration lines to the httpd.conf.


Apache Performance Tuning Issues

• Three Rules of thumb:– Make sure your server has enough physical

resources: Fast Disk and enough RAM– Make sure you have enough bandwidth– Make Apache do as little work as it has to do.


Server Requirements

• Generally, the more requests you server has to concurrently handle, the more horsepower it must have.

• More requests = More Access to Disk (Get lots of fast disk)

• More requests = More Apache processes = More RAM (Get lots of RAM)


Assessing Apache RAM Requirements

• Apache will create a number of child processes upon startup and create more of them as needed.

• 1 child process required for each client request• Generally, each Apache child process will take up 2-5

MB of RAM. Therefore, you can make RAM estimates:– RAM Usage = (Apache Process Size) X (Max current users)

• Using dynamic content like CGI scripts, Server Side Includes, etc. will require more memory and CPU power.


RAM Requirements, etc.

• If you expect a maximum of 25 simultaneous requests to your server and the size of each Apache process is 4MB, you will need at least 100MB dedicated to Apache.

• The size of each Apache process will vary from machine to machine, depending on the modules used, the machine architecture, etc.

• You can asses the real size of your Apache process (httpd) by using a system monitoring utility like top.


Bandwidth Requirements• It’s important to know whether you have enough

bandwidth to handle your web requests.• The “fatter the pipe”, the quicker contents can be

delivered.• Requirements differ depending on contents: rich

multimedia (many graphics, streaming audio/video) requires more bandwidth.

• Other network concepts such as website latency can play into overall website performance.


Making Apache Do As Little as Possible….

• Removing features from Apache during compilation and from the httpd.conf after compilation can help increase Apache’s performance and memory requirements.– Compiling in additional and/or unnecessary

modules can slow Apache’s performance and increase memory requirements.


Resources on Apache Performance Tuning

• Book: Web Performance Tuning: Speeding Up the Web, Killelea - O’Reilly 1998

• CU’s white paper on Apache Performance Tuning

• Apache performance notes: http://httpd.apache.org/docs/misc/perf-tuning.html (some very detailed, low-level technical details)

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