Computer Systems Security, Schemes and Mind Maps of Computer Security

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Computer Security:

Principles and Practice

Fourth Edition

By: William Stallings and Lawrie Brown

Chapter 10

Buffer Overflow

Buffer Overflow

• A very common attack mechanism
  • First widely used by the Morris Worm in 1988
• Prevention techniques known
• Still of major concern
  • Legacy of buggy code in widely deployed operating systems and applications
  • Continued careless programming practices by programmers

Buffer Overflow A buffer overflow, also known as a buffer overrun, is defined in the NIST Glossary of Key Information Security Terms as follows: “A condition at an interface under which more input can be placed into a buffer or data holding area than the capacity allocated, overwriting other information. Attackers exploit such a condition to crash a system or to insert specially crafted code that allows them to gain control of the system.”

Programming Language History

• At the machine level data manipulated by machine instructions executed by the computer processor are stored in either the processor’s registers or in memory
• Assembly language programmer is responsible for the correct interpretation of any saved data value Modern high-level languages have a strong notion of type and valid operations - (^) Not vulnerable to buffer overflows - (^) Does incur overhead, some limits on use C and related languages have high- level control structures, but allow direct access to memory • (^) Hence are vulnerable to buffer overflow
• (^) Have a large legacy of widely used, unsafe, and hence vulnerable

Stack Buffer Overflows

• Occur when buffer is located on stack
  • Also referred to as^ stack smashing
  • Used by Morris Worm
  • Exploits included an unchecked buffer overflow
• Are still being widely exploited
• Stack frame
  • When one function calls another it needs somewhere to save the return address
  • Also needs locations to save the parameters to be passed in to the called function and to possibly save register values

Figure 10. Another Stack Overflow Example

Table 10. Some Common Unsafe C Standard Library Routines

Figure

Example UNIX Shellcode

Table 10. Some Common x86 Assembly Language Instructions