How do Arrays and more work in C¶

C Arrays & Pointers

Arrays in C are essentially pointers.
Nothing is checked by the compiler. You can do whatever you want. There are no boundaries in C.

Example:

int array[5] = {1, 2, 3, 4, 5};
array[0] = 0;
array[4] = 0;

Pointers can be used to manipulate array elements:
```
int *a = array;
a[2] = 0;
```

Copying Data

Functions to copy strings:

strcpy(destination, source);
memcpy(destination, source, len);
gets(destination);

Vulnerabilities arise when the destination buffer size is not considered, leading to buffer overflows.

Exploitation Basics

Common vulnerability: Buffer overflow due to functions like strcpy() not considering the destination buffer size.

Example:

char destination[8];
char source[16] = "1234567890123456\x00";
strcpy(destination, source);

Non-Arrays in C

C has basic types (int, float), enumerated types, void type, and derived types (pointers, arrays, structures, unions, functions).
Arrays consist of multiple elements of the same type.
Structures can hold multiple elements of different types.

Example:

struct var {
    short x;
    long y;
    char z[3];
}

Remember

Conclusion

C does not enforce buffer boundaries, making it susceptible to buffer overflow attacks.
strcpy() and similar functions do not check the size of the destination buffer, leading to potential overwrites of adjacent memory.
One buffer can overflow into another buffer
Local variables/buffers are adjoin to each other
Pointer can point to any memory address