the-web-application-hackers-handbook

134 Chapter 5 n Bypassing Client-Side Controls
machine is intriguing. If any aspect of the game play is controlled within the
client instead of by the server, an attacker could manipulate the game with
precision to improve the odds, change the rules, or alter the scores submitted
to the server. Several kinds of attacks could occur in this scenario:
n The client component could be trusted to maintain the game state. In this
instance, local tampering with the game state would give an attacker an
advantage in the game.
n An attacker could bypass a client-side control and perform an illegal action
designed to give himself an advantage within the game.
n An attacker could find a hidden function, parameter, or resource that,
when invoked, allows illegitimate access to a server-side resource.
n If the game involves any peers, or a house player, the client component
could be receiving and processing information about other players that,
if known, could be used to the attacker’s advantage.
Common Browser Extension Technologies
The browser extension technologies you are most likely to encounter are Java
applets, Flash, and Silverlight. Because these are competing to achieve similar
goals, they have similar properties in their architecture that are relevant to
security:
n They are compiled to an intermediate bytecode.
n They execute within a virtual machine that provides a sandbox environment
for execution.
n They may use remoting frameworks employing serialization to transmit
complex data structures or objects over HTTP.
Java
Java applets run in the Java Virtual Machine (JVM) and are subject to the sandboxing
applied by the Java Security Policy. Because Java has existed since early
in the web’s history, and because its core concepts have remained relatively
unchanged, a large body of knowledge and tools are available for attacking and
defending Java applets, as described later in this chapter.
Flash
Flash objects run in the Flash virtual machine, and, like Java applets, are sandboxed
from the host computer. Once used largely as a method of delivering
animated content, Flash has moved on. With newer versions of ActionScript,