We start with the obvious approach of preventing them by not writing code that is vulnerable to buffer overflows in the first place. Next we consider ways of defending against buffer overflow attacks. We continue with an overview of the purpose and design of shellcode, which is the custom code injected by an attacker and to which control is transferred as a result of the buffer overflow. This includes a discussion of how functions store their local variables on the stack and the consequence of attempting to store more data in them than there is space available. Then we present details of the classic stack buffer overflow. We begin with an introduction to the basics of buffer overflow. ![]() ![]() This chapter focuses on how a buffer overflow occurs and what methods can be used to prevent or detect its occurrence. Unfortunately, due to both a legacy of buggy code in widely deployed operating systems and applications and continuing careless programming practices by programmers, it is still a major source of concern to security practitioners. modified from slides of Lawrie BrownĢ Buffer Overflow a very common attack mechanismįirst wide use by the Morris Worm in 1988 prevention techniques known still of major concern legacy of buggy code in widely deployed operating systems and applications Shellshock, Hearthbleed continued careless programming practices by programmers Yet this type of attack has been known since it was first widely used by the Morris Internet Worm in 1988, and techniques for preventing its occurrence are well known and documented. These can result in exploits to both operating systems and common applications. ![]() Similarly, several of the items in the CWE/SANS Top 25 Most Dangerous Software Errors list, Risky Resource Management category, are buffer overflow variants. A look at the list of vulnerability advisories from organizations such as CERT or SANS continue to include a significant number of buffer overflow or heap overflow exploits, including a number of serious, remotely exploitable vulnerabilities. This type of attack is one of the most common attacks seen and results from careless programming in applications. In this chapter we turn our attention specifically to buffer overflow attacks.
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