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

364 Chapter 16 Web Application Security
personal information as to what securities the users hold and how much of each, and in
extreme cases, even bank account information for users.
Even the exposure of a table full of names and addresses is a serious violation of security.
Customers value their privacy very highly, and a huge list of names and addresses,
plus some inferred information about them (“all ten thousand of these people like to
shop at online tobacco stores”) creates a potential sellable item to marketing firms that
do not play by the rules.
Much worse than simple access to our data, of course, is if somebody finds a way to
manipulate them. A happy bank customer might find his account a few thousand dollars
richer, or customer shipping addresses might be modified, causing some happy person
somewhere (presumably one of the people who changed the data) to receive a good
number of packages that should have been sent elsewhere.
Loss or Destruction of Data
Every bit as bad as having unauthorized users gain access to sensitive data is if we suddenly
find that some portion of our data has been deleted or destroyed. If somebody
manages to destroy tables in our database, our business could face irrecoverable consequences.
If we are an online bank that displays bank account information, and somehow
all the information for a particular account is lost, we are not a good bank. Much worse,
if the entire table of users is deleted, we will find ourselves spending a large amount of
time reconstructing databases and finding out who owns what.
It is important to note that loss or destruction of data does not have to come from
malicious or accidental misuse of our system. If the building in which our servers are
housed burns down, and all the servers and hard disks with it, we have lost a large
amount of data and had better hope that we have adequate backups and disaster recovery
plans.
Denial of Service
We have previously talked about denial of service attacks (DoS) and their more serious
cousins, distributed denial of service attacks (DDos) as potentially devastating attacks on
our application’s availability. Having your servers rendered useless for hours, if not longer,
can be a serious burden from which to recover. If you consider how ubiquitous many of
the major sites on the Internet are and how you always expect them to be there, any
downtime is a problem.
Again, as in the previous section, a DoS can come from forces other than misuse.
Even if we have robust backups stored off-site, if the building with our servers in it
burns down, is buried in a mudslide, or is destroyed by alien invaders, and we do not
have a plan for getting those computers back online extremely rapidly, we might find
ourselves losing customers for days.