Buffer Overflow

Buffer Overflow

In a buffer Over flow while writing data to a buffer, the buffer boundary is over run and adjacent memory is over written

In computer security and programming, a buffer overflow, or buffer overrun, is an anomaly where a program, while writing data to a buffer, overruns the buffer's boundary and overwrites adjacent memory locations. This is a special case of the violation of memory safety.

A buffer overflow occurs when data written to a buffer also corrupts data values in memory addresses adjacent to the destination buffer due to insufficient bounds checking. This can occur when copying data from one buffer to another without first checking that the data fits within the destination buffer.

 a program has two data items which are adjacent in memory: an 8-byte-long string buffer

EXPLOITATION

The techniques to exploit a buffer overflow vulnerability vary by architecture, by operating system and by memory region. For example, exploitation on the heap differs markedly from exploitation on the call stack.

1. Heap-based exploitation
2. Barriers to exploitation
3. Practicalities of exploitation

char           A[8] = "";
unsigned short B    = 1979;

Initially, A contains nothing but zero bytes, and B contains the number 1979.

strcpy

"excessive" is 9 characters long and encodes to 10 bytes including the terminator, but A can take only 8 bytes. By failing to check the length of the string, it also overwrites the value of B:

strncpy(A, "excessive", sizeof(A));

To prevent the buffer overflow from happening in this example, it would be best to replace the strcpy call with a strncpy, which takes the maximum capacity of A as an additional parameter and ensures that no more than this amount of data is written to A