“It doesn’t take more than two weeks before a major application,
part of most Linux distributions, presents a security hole,
allowing, for instance, a local user to become root. Despite the
great quality of most of this software, ensuring the security of a
program is a hard job : it must not allow a bad guy to benefit
illegally from system resources. The availability of application
source code is a good thing, much appreciated by programmers, but
the smallest defect in a software becomes visible to everyone.
Furthermore, the detection of such defects comes at random and
people doing that sort of things do not always act with good
intentions.”
“From the sysadmin side, daily work consists of reading the
lists concerning security problems and updating immediately the
involved packages. For a programmer it can be a good lesson to try
out such security problems. Avoiding security holes from the
beginning is preferred. We’ll try to define some “classic”
dangerous behaviors and provide solutions to reduce the risks. We
won’t talk about network security problems since they often come
from configuration mistakes (dangerous cgi-bin scripts, …) or
from system bugs allowing DOS (Denial Of Service) type attacks to
prevent a machine from listening to its own clients. These problems
concern the sysadmin or the kernel developers, but the application
programmer too, as soon as he takes into account external data. For
instance, pine, acroread, netscape, access,… on some versions
under some conditions allowed remote access or information leaks.
As a matter of fact secure programming is everyone’s concern.”
“This set of articles shows methods which can be used to damage
an Unix system. We could only have mentioned them or said a few
words about them, but we prefer open explanations to make people
understand the risks. Thus, when debugging a program or developing
your own, you’ll be able to avoid or correct these mistakes. For
each discussed hole, we will take the same approach. We’ll start
detailing the way it works. Next, we will show how to avoid it. For
every example we will use security holes still presents in wide
spread software.”