Web Server Administration
Chapter 10
Securing the Web Environment
Overview
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Identify threats and vulnerabilities
Secure data transmission
Secure the operating system
Secure server applications
Overview
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Authenticate Web users
Use a firewall
Use a proxy server
Use intrusion detection software
Identifying Threats and
Vulnerabilities
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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
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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
Examining TCP/IP
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Hackers often take advantage of the intricacy
of TCP/IP
The following are parts of the IP header most
relevant to security
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Source address
Destination address
Packet identification, flags, fragment offset
Total length
Protocol – TCP, UDP, ICMP
TCPDelivering Data to Applications
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Important header fields
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Source and destination ports
Sequence number, data offset
Flags, such as SYN, ACK, FIN
Establishing a TCP connection
Vulnerabilities of DNS
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Historically DNS has had security
problems
BIND is the most common
implementation of DNS and some older
version had serious bugs
BIND 9, the current version, has been
more secure
Vulnerabilities in Operating
Systems
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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
Vulnerabilities in Web servers
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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
Vulnerabilities of E-mail
Servers
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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
Digital communication
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Closed and secure (national defense,
VPN)
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Open and secure (SSL)
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Open and non-secure (PKI)
What Is PKI?
A PKI is an asymmetric cryptography
security environment that supports the
transmission, delivery, and receipt of
digital communications over a nonsecure communications channel.
PKI a ‘hot technology”
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E-Commerce
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E-Governance
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State of Illinois
What Does PKI Do?
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Authenticates sender of digital
communications
Protects integrity of digital communications
Key Pair
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Private
Public
Trusted third party
How PKI Works in Digital
Communications
Securing Data Transmission
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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)
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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
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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
Using SSH for Tunneling
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Tunneling allows you to use an unsecure
protocol, such as POP3, through a secure
connection, such as SSH
To set up tunneling
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Configure the SSH client so the local port is 55555
(or another port between 1024 and 65535)
Configure the SSH client to connect to POP3 port
110
Log in to the SSH client
Direct the e-mail client to port 5555 and log in to
the e-mail server
Securing the Operating
System
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Use the server for only necessary tasks
Minimize user accounts
Disable services that are not needed
Make sure that you have a secure password
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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
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There are many services that are not needed in
Windows for most Internet-based server applications
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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
Securing Linux
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As with Windows, make sure that you only
run daemons (services) that you need
Generally, daemons are disabled by default
The command netstat -l gives you a list of
daemons that are running
Use chkconfig to enable and disable daemons
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chkconfig imap on would enable imap
Securing E-mail
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You have already seen the ability to
tunnel POP3 which would prevent data
from being seen
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 the Web Server
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Enable the minimum features
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If you don't need a programming
language, do not enable it
Make sure programmers understand
security issues
Implement SSL where appropriate
Configuring User
Authentication in IIS
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Four types of authenticated access
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Windows integrated authentication
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Digest authentication for Windows domain servers
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Works with proxy servers
Requires Active Directory and IE
Basic authentication
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Most secure – requires IE
User name and password in clear text
Works with IE, Netscape, and others
Passport authentication
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Centralized form of authentication
Only available on Windows Server 2003
Using a Firewall
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A firewall implements a security policy
between networks
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Our focus is between the Internet and an
organization's network
You need to limit access, especially
from the Internet to your internal
computers
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Restrict access to Web servers, e-mail
servers, and other related servers
Types of Filtering
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Packet filtering
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Circuit-level filtering (stateful or dynamic filtering)
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Looks at each individual packet
Based on rules, it determines whether to let it pass through
the firewall
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
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Instead of transferring packets, it sets up a separate
connection to totally isolate applications such as Web and email
A Packet-filtering Firewall
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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
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Drop – (best) thrown away without response
Reject – ICMP message sent in response
Summary
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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