O'Reilly Securing AJAX Applications

247 Pages·2007·1.94 MB·English

Securing Ajax Applications
Christopher Wells
Beijing • Cambridge • Farnham • Köln • Paris • Sebastopol • Taipei • Tokyo
Securing Ajax Applications
by Christopher Wells
Copyright © 2007 Christopher Wells. All rights reserved.
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ISBN-10: 0-596-52931-7
ISBN-13: 978-0-596-52931-4
[M]
To Jennafer, my honey, and Maggie, my bit of
honey:
you two are what make life so sweet.

Table of Contents
Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ix
1. The Evolving Web . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
The Rise of the Web 2
2. Web Security . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Security Basics 29
Risk Analysis 37
Common Web Application Vulnerabilities 40
3. Securing Web Technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
How Web Sites Communicate 56
Browser Security 61
Browser Plug-ins, Extensions, and Add-ons 76
4. Protecting the Server . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
Network Security 100
Host Security 103
Web Server Hardening 121
Application Server Hardening 128
5. A Weak Foundation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130
HTTP Vulnerabilities 131
The Threats 136
JSON 143
XML 146
RSS 148
Atom 149
REST 152
vii
6. Securing Web Services . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155
Web Services Overview 156
Security and Web Services 167
Web Service Security 172
7. Building Secure APIs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174
Building Your Own APIs 174
Preconditions 179
Postconditions 180
Invariants 180
Security Concerns 181
RESTful Web Services 183
8. Mashups . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190
Web Applications and Open Internet APIs 191
Wild Web 2.0 192
Mashups and Security 194
Open Versus Secure 198
A Security Blanket 199
Case Studies 201
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213
viii | Table of Contents
Preface
1
Deciding to add security to a web application is like deciding whether to wear
clothes in the morning. Both decisions provide comfort and protection throughout
theday,andinbothcasesthedecisionsarebettermadebeforehandratherthanlater.
Justlookaroundandaskyourself,“HowopendoIreallywanttobewithmyneigh-
bors?” Or, “How open do I really want them to be with me?”
It’s all about sharing. With web sites sharing data via open APIs, web services, and
other new technologies we are experiencing the veritable Woodstock of the digital
age. Free love now takes the form of free content and services. Make mashups, not
web pages! All right, so let’s get down to business.
Believe it, or not, there is security in openness. Look at the United States govern-
ment,forexample.TheopennessoftheU.S.governmentalsystemiswhathelpskeep
it secure. Maybe that can work for us, too! Repeat after me:
We,theprogrammers,inordertobuildamoreperfectWeb;toestablishpresenceand
ensure server stability; provide for the common Web; promote general security; for
ourselves and our posterity; do ordain and establish this constitution…
Sadly,itisnotquitethateasy—orisit?Checksandbalancesmakegovernmentswork.
There are layers of cooperation and defense. Each layer provides defense in depth.
Webapplicationsecurityisaseriousbusiness.Allwebapplicationsareorwillbevul-
nerable to some form of attack. The thing to remember is that most people are good,
andsecurityisimplementedtothwartthosewhoarenot.So,thechancesofyourappli-
cation getting attacked are proportional to the number of bad apples out there.
Audience
This book is for programmers on the front lines looking for a solid resource to help
them protect their applications from harm. It is also for the developer or architect
interested in sharing or consuming content in a safe way.
ix
Assumptions This Book Makes
This book assumes basic developers’ knowledge of the Internet and web applica-
tions. It also assumes a general awareness of security problems that can arise on the
Internet. Knowledge of security methodologies and practices is helpful, but not
required.
Contents of This Book
Chapter1,The Evolving Web
Recounts how we got to where we are today on the Web. The chapter explains
how web technologies have evolved, and why we have such a tangled Web.
Chapter2,Web Security
Describesbasicsecurityterms,practices,andmethodologies.Italsolaysoutand
identifies the major vulnerabilities on the Web today.
Chapter3,Securing Web Technologies
Describes all the different types of web communications. This chapter discusses
basic security measures that minimize risk and examines the security of several
Internet technologies.
Chapter4,Protecting the Server
Walks through setting up a secure web server. It offers practical advice to help
protect a server from threats on the Internet.
Chapter5,A Weak Foundation
Exploresthemajorprotocolsassociatedwithwebapplications,wheretheseams
are,whatthepossibleattackvectorsmightbe,andsomerecommendedcounter-
measures to help make applications more secure.
Chapter6,Securing Web Services
Looks at how web services work, the moving parts, how web technologies such
as Ajax can fit in, and what major areas require security attention.
Chapter7,Building Secure APIs
ExamineswebAPIdesignandconstructionandpointsoutsomesecuritypitfalls
along the way.
Chapter8,Mashups
DiscussestheevolutionofwebAPIsandhowtheywork.Thischapteralsolooks
at some of the major security issues with mashups, such as lack of trust and
authentication. It also tries to answer questions, such as what is the worst that
can happen, and how to balance openness and security.
x | Preface
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Using Code Examples
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We appreciate, but do not require, attribution. An attribution usually includes the
title, author, publisher, and ISBN. For example: “Securing Ajax Applications by
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Preface | xi
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Acknowledgments
I would like to extend my thanks to the great folks at O’Reilly for giving me the
opportunity to write this book. I would especially like to thank my editor, Tatiana
Apandi,forputtingupwithme,andtoallthetechnicalreviewerswhoreadmybook
and provided such instructive feedback. Thank you.
IwouldalsoliketothankMickBauer,whosebook,LinuxServerSecurity:Toolsand
Best Practices for Bastion Hosts (O’Reilly), has served as a great inspiration (if you
run Linux, read it).
xii | Preface