Web Server Administration

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31 Οκτ 2013 (πριν από 3 χρόνια και 5 μήνες)

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Web Server Administration

TEC 236

Securing the Web Environment


Identify threats and vulnerabilities

Secure data transmission

Secure the operating system

Secure server applications


Authenticate Web users

Use a firewall

Use a proxy server

Use intrusion detection software

Identifying Threats and

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

Often, operating system flaws can assist the

Vulnerabilities in Operating

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

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

Securing the Operating

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

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


Computer browser

DHCP client

DNS client




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

Vulnerabilities of E

By design, e
mail servers are open

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

Exchange 2000 can also use SSL for the
protocols it uses

To prevent someone from sending large
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

Vulnerabilities in Web servers

Static HTML pages pose virtually no

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


The URLScan utility blocks potentially harmful page

The IIS Lockdown utility has templates to ensure that
you only enable what you need

Change NTFS permissions in
wwwroot from
Everyone Full Control to Everyone Execute

In IIS 5, delete
IISHelp and

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

Restrict access to Web servers, e
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

level filtering (stateful or dynamic filtering)

Controls complete communication session, not just individual

Allows traffic initialized from within the organization to
return, yet restricts traffic initialized from outside


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

A Packet
filtering Firewall

Consists of a list of acceptance and denial

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


(best) thrown away without response


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

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

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

In Linux, Tripwire tracks changes to


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


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

The following intrusions are tracked

Windows out
band (WinNuke)

A specific type of Denial
Service attack


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.


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

Keep applications and services to a minimum


User authentication controls access to one or
more Web server directories

Firewalls control access policies between

A proxy server delivers content on behalf of a
user or server application

Intrusion detection software identifies
intrusions but typically does not prevent them