Web Server AdministrationTEC 236

Securing the Web Environment

Overview

Identify threats and vulnerabilities Secure data transmission Secure the operating system Secure server applications

Overview

Authenticate Web users Use a firewall Use a proxy server Use intrusion detection software

Identifying Threats and Vulnerabilities Focus is on threats from the Internet Hackers sometimes want the challenge

of penetrating a system and vandalizing it – other times they are after data Data can be credit card numbers, user

names and passwords, other personal data Information can be gathered while it is

being transmitted Often, operating system flaws can assist

the hacker

Vulnerabilities in Operating Systems Operating systems are large and complex

which means that there are more opportunities for attack

Although Windows has had its share of problems, often inattentive administrators often fail to implement patches when available

Some attacks, such as buffer overruns, can allow the attacker to take over the computer

Securing the Operating System Use the server for only necessary tasks Minimize user accounts Disable services that are not needed Make sure that you have a secure password

In addition to using upper case, lower case numbers and symbols, hold down the ALT key on a number (on the numeric keypad) from 1 to 255

Check a table of ALT values to avoid common characters

The use of the ALT key will thwart most hackers

Securing Windows There are many services that are not needed

in Windows for most Internet-based server applications

Alerter Computer browser DHCP client DNS client Messenger Server Workstation

Also, the registry can be used to alter the configuration to make it more secure such as disabling short file names

Vulnerabilities of E-mail Servers By design, e-mail servers are open E-mail servers can be harmed by a

series of very large e-mail messages Sending an overwhelming number of

messages at the same time can prevent valid users from accessing the server

Viruses can be sent to e-mail users Retrieving e-mail over the Internet often

involves sending your user name and password as clear text

Securing E-mail

Exchange 2000 can also use SSL for the protocols it uses

To prevent someone from sending large e-mail messages until the disk is full, set a size limit for each mailbox

Securing Data Transmission To secure data on a network that is

accessible to others, you need to encrypt the data

SSL is the most common method of encrypting data between a browser and Web server

Secure Shell (SSH) is a secure replacement for Telnet

Secure Sockets Layer (SSL) A digital certificate issued by a certification

authority (CA) identifies an organization The public key infrastructure (PKI) defines

the system of CAs and certificates Public key cryptography depends on two

keys A public key is shared with everyone The public key can be used to encrypt data Only the owner of the public key has the

corresponding private key which is needed to decrypt the data

Establishing an SSL Connection

Vulnerabilities in Web servers

Static HTML pages pose virtually no problem

Programming environments and databases add complexity that a hacker can exploit

Programmers often do not have time to focus on security

Securing the Web Server

Enable the minimum features If you don't need a programming

language, do not enable it Make sure programmers

understand security issues Implement SSL where appropriate

Securing the Web Server-IIS The URLScan utility blocks potentially harmful

page requests The IIS Lockdown utility has templates to

ensure that you only enable what you need Change NTFS permissions in \inetpub\wwwroot

from Everyone Full Control to Everyone Execute

In IIS 5, delete \samples \IISHelp and \MSADC folders

Delete extensions you do not use, such as .htr, .idc, .stm, and others

Authenticating Web Users

Both Apache and IIS use HTTP to enable authentication HTTP tries to access a protected

directory and fails Then it requests authentication from the

user in a dialog box Accesses directory with user information

Used in conjunction with SSL

Configuring User Authentication in IIS Four types of authenticated access

Windows integrated authentication Most secure – requires IE

Digest authentication for Windows domain servers

Works with proxy servers Requires Active Directory and IE

Basic authentication User name and password in clear text Works with IE, Netscape, and others

Passport authentication Centralized form of authentication Only available on Windows Server 2003

Using a Firewall A firewall implements a security

policy between networks Our focus is between the Internet and

an organization's network You need to limit access, especially

from the Internet to your internal computers Restrict access to Web servers, e-mail

servers, and other related servers

Types of Filtering Packet filtering

Looks at each individual packet Based on rules, it determines whether to let it pass

through the firewall Circuit-level filtering (stateful or dynamic

filtering) Controls complete communication session, not just

individual packets Allows traffic initialized from within the organization

to return, yet restricts traffic initialized from outside Application-level

Instead of transferring packets, it sets up a separate connection to totally isolate applications such as Web and e-mail

A Packet-filtering Firewall Consists of a list of acceptance and

denial rules A firewall independently filters what

comes in and what goes out It is best to start with a default policy

that denies all traffic, in and out We can reject or drop a failed packet

Drop – (best) thrown away without response Reject – ICMP message sent in response

Using a Proxy Server A proxy server delivers content on behalf of a

user or server application Proxy servers need to understand the protocol of

the application that they proxy such as HTTP or FTP

Forward proxy servers isolate users from the Internet

Users contact proxy server which gets Web page Reverse proxy servers isolate Web server

environment from the Internet When a Web page is requested from the Internet, the

proxy server retrieves the page from the internal server

Using Intrusion Detection Software

Intrusion detection is designed to show you that your defenses have been penetrated

With Microsoft ISA Server, it only detects specific types of intrusion

In Linux, Tripwire tracks changes to files

Tripwire Tripwire allows you to set policies that

allow you to monitor any changes to the files on the system

Tripwire can detect file additions, file deletions, and changes to existing files

By understanding the changes to the files, you can determine which ones are unauthorized and then try to find out the cause of the change

Tripwire After installing Tripwire, you configure

the policy file to determine which files to monitor

A default list of files is included but it will take time to refine the list

A report can be produced to find out which files have been added, changed, and deleted Usually, it runs automatically at night

Intrusion Detection in ISA Server The following intrusions are tracked Windows out-of-band (WinNuke)–A specific type of Denial-

of-Service attack Land–A spoofed packet is sent with the SYN flag set so that

the source address is the same as the destination address, which is the address of the server. The server can then try to connect to itself and crash.

Ping of death –The server receives ICMP packets that include large files attachments, which can cause a server to crash.

IP half scan –If a remote computer attempts to connect to a port by sending a packet with the SYN flag set and the port is not available, the RST flag is set on the return packet. When the remote computer does not respond to the RST flag, this is called an IP half scan. In normal situations, the TCP connection is closed with a packet containing a FIN flag.

UDP bomb –A UDP packet with an illegal configuration. Port scan –You determine the threshold for the number of

ports that are scanned (checked) before an alert is issued.

Summary Every computer connected to the Internet

represents a potential target for attack Hackers can gather data and modify

systems SSL can secure data transmission Keep each server to a single purpose such

as Web server or e-mail Keep applications and services to a

minimum

Summary User authentication controls access to

one or more Web server directories Firewalls control access policies

between networks A proxy server delivers content on

behalf of a user or server application Intrusion detection software identifies

intrusions but typically does not prevent them