Protostar Stack5

Here are the instructions for the challenge

About
Stack5 is a standard buffer overflow, this time introducing shellcode.

This level is at /opt/protostar/bin/stack5

Hints

At this point in time, it might be easier to use someone elses shellcode
If debugging the shellcode, use \xcc (int3) to stop the program executing and return to the debugger
remove the int3s once your shellcode is done.
#include <stdlib.h>
#include <unistd.h>
#include <stdio.h>
#include <string.h>

int main(int argc, char **argv)
{
  char buffer[64];

  gets(buffer);
}

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Protostar Stack4

Here are the instructions for the challenge

About
Stack4 takes a look at overwriting saved EIP and standard buffer overflows.

This level is at /opt/protostar/bin/stack4

Hints

A variety of introductory papers into buffer overflows may help.
gdb lets you do “run < input”
EIP is not directly after the end of buffer, compiler padding can also increase the size.
#include <stdlib.h>
#include <unistd.h>
#include <stdio.h>
#include <string.h>

void win()
{
  printf("code flow successfully changed\n");
}

int main(int argc, char **argv)
{
  char buffer[64];

  gets(buffer);
}

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Protostar Stack3

Here are the instructions for the challenge

About
Stack3 looks at environment variables, and how they can be set, and overwriting function pointers stored on the stack (as a prelude to overwriting the saved EIP)

Hints

both gdb and objdump is your friend you determining where the win() function lies in memory.
This level is at /opt/protostar/bin/stack3
#include <stdlib.h>
#include <unistd.h>
#include <stdio.h>
#include <string.h>

void win()
{
  printf("code flow successfully changed\n");
}

int main(int argc, char **argv)
{
  volatile int (*fp)();
  char buffer[64];

  fp = 0;

  gets(buffer);

  if(fp) {
      printf("calling function pointer, jumping to 0x%08x\n", fp);
      fp();
  }
}

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Protostar Stack2

Here are the instructions for the challenge

About
Stack2 looks at environment variables, and how they can be set.

This level is at /opt/protostar/bin/stack2
#include <stdlib.h>
#include <unistd.h>
#include <stdio.h>
#include <string.h>

int main(int argc, char **argv)
{
  volatile int modified;
  char buffer[64];
  char *variable;

  variable = getenv("GREENIE");

  if(variable == NULL) {
      errx(1, "please set the GREENIE environment variable\n");
  }

  modified = 0;

  strcpy(buffer, variable);

  if(modified == 0x0d0a0d0a) {
      printf("you have correctly modified the variable\n");
  } else {
      printf("Try again, you got 0x%08x\n", modified);
  }

}

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Protostar Stack1

Here are the instructions for the challenge

About
This level looks at the concept of modifying variables to specific values in the program, and how the variables are laid out in memory.

This level is at /opt/protostar/bin/stack1

Hints

If you are unfamiliar with the hexadecimal being displayed, “man ascii” is your friend.
Protostar is little endian
#include <stdlib.h>
#include <unistd.h>
#include <stdio.h>
#include <string.h>

int main(int argc, char **argv)
{
  volatile int modified;
  char buffer[64];

  if(argc == 1) {
      errx(1, "please specify an argument\n");
  }

  modified = 0;
  strcpy(buffer, argv[1]);

  if(modified == 0x61626364) {
      printf("you have correctly got the variable to the right value\n");
  } else {
      printf("Try again, you got 0x%08x\n", modified);
  }
}

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Protostar Stack0

I’m going to start the second challenge ISO from exploit-exercises.com. These challenges deal more with exploit development and reverse engineering.

Here are the instructions for the first challenge called Stack0

About
This level introduces the concept that memory can be accessed outside of its allocated region, how the stack variables are laid out, and that modifying outside of the allocated memory can modify program execution.

This level is at /opt/protostar/bin/stack0
#include <stdlib.h>
#include <unistd.h>
#include <stdio.h>

int main(int argc, char **argv)
{
  volatile int modified;
  char buffer[64];

  modified = 0;
  gets(buffer);

  if(modified != 0) {
      printf("you have changed the 'modified' variable\n");
  } else {
      printf("Try again?\n");
  }
}

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