This level advances from format2 and shows how to write more than 1 or 2 bytes of memory to the process. This also teaches you to carefully control what data is being written to the process memory.
This level is at /opt/protostar/bin/format3
#include <stdlib.h>
#include <unistd.h>
#include <stdio.h>
#include <string.h>
int target;
void printbuffer(char *string)
{
printf(string);
}
void vuln()
{
char buffer[512];
fgets(buffer, sizeof(buffer), stdin);
printbuffer(buffer);
if(target == 0x01025544) {
printf("you have modified the target :)\n");
} else {
printf("target is %08x :(\n", target);
}
}
int main(int argc, char **argv)
{
vuln();
}