BugTraq
libwmf integer/heap overflow Jun 30 2006 07:03AM
sean (infamous41md hotpop com)
Sorry I don't have time to chase down multiple email addresses of alleged
developers; so here this is after weeks of no response. POC is not attached
unlike advisory says. It's not very difficult to exploit.

++++++++++++++++++++++++++++++++++++++++++++

Subject:

libwmf integer/heap overflow

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Product:

libwmf is a library for reading vector images in Microsøft's native Windøws
Metafile Format (WMF) and for either (a) displaying them in, e.g., an X window;
or (b) converting them to more standard/open file formats such as, e.g., the
W3C's XML-based Scaleable Vector Graphic (SVG) format.

http://wvware.sourceforge.net/libwmf.html

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Vulnerable:

I tested the most recent release, 0.2.8.4

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Summary:

An integer overflow in memory allocation leads to a heap overflow.

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Details:

------------------------------------------------------------------------
-------
file: src/meta.c +117
------------------------------------------------------------------------
-------

wmf_error_t wmf_header_read (wmfAPI* API)
{ U16 u16a;
U16 u16b;

...snip...

if (API->File->wmfheader->HeaderSize == 9)
{ API->File->wmfheader->Version = wmf_read_16 (API);
API->File->wmfheader->FileSize = wmf_read_32 (API,0,0);
API->File->wmfheader->NumOfObjects = wmf_read_16 (API);
1] API->File->wmfheader->MaxRecordSize = wmf_read_32 (API,0,0);
API->File->wmfheader->NumOfParams = wmf_read_16 (API);

1) This value is taken directly from the wmf file, later it will be used
to allocate memory. It is not sanitized at any point.

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

------------------------------------------------------------------------
-------
file: src/player.c +86
------------------------------------------------------------------------
-------

wmf_error_t wmf_scan (wmfAPI* API,unsigned long flags,wmfD_Rect* d_r)
{ wmfPlayer_t* P = (wmfPlayer_t*) API->player_data;

...snip...

wmf_header_read (API);

...snip...

1]

/* P->Parameters = (unsigned char*) wmf_malloc (API,(MAX_REC_SIZE
(API)-3) * 2 * sizeof (unsigned char)); */ P->Parameters = (unsigned
char*) wmf_malloc (API,(MAX_REC_SIZE(API) ) * 2 * sizeof (unsigned
char)); /* HOLE */

WmfPlayMetaFile (API);

1) Overflow the calculation.

**************************

static wmf_error_t WmfPlayMetaFile (wmfAPI* API)
{ int i;
int byte;
int changed;

unsigned char* Par;

...snip...

1] Par = P->Parameters;

...snip...

number = 0;
do
{ if (++number < API->store.count)
{ atts = API->store.attrlist + number;
}
else
{ atts = &attrlist;
wmf_attr_clear (API, atts);
}

2] Size = wmf_read_32 (API,0,0);
Function = wmf_read_16 (API);

if ((Size == 3) && (Function == 0))
{ if (SCAN (API)) wmf_write (API, Size, Function,
"empty", atts->atts, 0, 0);
break; /* Probably final record ?? */
}

/* if ((Size > MAX_REC_SIZE (API)) || (Size < 3))
*/ if (((Size - 3) > MAX_REC_SIZE (API)) || (Size < 3))
{ WMF_ERROR (API,"libwmf: wmf with bizarre record size;
bailing..."); WMF_ERROR (API," please send it to us at
http://www.wvware.com/"); wmf_printf (API,"maximum record size = %u\n",
(unsigned) MAX_REC_SIZE (API)); wmf_printf (API,"record size = %u\n",(unsigned)
Size); API->err = wmf_E_BadFormat;
break;
}

pos_params = WMF_TELL (API);

if (pos_params < 0)
{ WMF_ERROR (API,"API's tell() failed on input stream!");
API->err = wmf_E_BadFile;
break;
}

3] for (i = 0; i < ((Size - 3) * 2); i++)
{ byte = WMF_READ (API);
if (byte == (-1))
{ WMF_ERROR (API,"Unexpected EOF!");
API->err = wmf_E_EOF;
break;
}
Par[i] = (unsigned char) byte; /* VECTOR */
}

1) Points to the memory we allocated above.

2) Controls the number of bytes we write into the buffer.

3) Overflow the buffer by arbitrarily huge amounts.

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

++++++++++++++++++++++++++++++++++++++++++++

Mitigating factors:

None.

++++++++++++++++++++++++++++++++++++++++++++

Workaround:

Do not open up untrusted wmf files.

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Notes:

libwmf is used by:

wv
abiword
freetype
gimp
libgsf
imagemagick

++++++++++++++++++++++++++++++++++++++++++++

Exploits:

POC is provided that crashes in free(). The easiest way to test is to use the
example conversion programs that come with libwmf, they are found in the
src/convert/.libs directory:

sean@hydra:~/libwmf-0.2.8.4/src/convert/.libs$ gcc -Wall exwmf.c
sean@hydra:~/libwmf-0.2.8.4/src/convert/.libs$ ./a.out > evil.wmf
sean@hydra:~/libwmf-0.2.8.4/src/convert/.libs$ gdb wmf2x
GNU gdb 6.3-debian

(gdb) r evil.wmf
Starting program: /home/sean/libwmf-0.2.8.4/src/convert/.libs/wmf2x evil.wmf
ERROR: player.c (482): Unexpected EOF!

Program received signal SIGSEGV, Segmentation fault.
0x402d5354 in mallopt () from /lib/libc.so.6
(gdb) bt
#0 0x402d5354 in mallopt () from /lib/libc.so.6
#1 0x402d415f in free () from /lib/libc.so.6
#2 0x402c283b in fclose () from /lib/libc.so.6
#3 0x4006e10e in wmf_file_close (API=0x804ad38) at bbuf.c:137
#4 0x4006d7d8 in wmf_lite_destroy (API=0x804ad38) at api.c:336
#5 0x40021e6f in wmf_api_destroy (API=0x804ad38) at wmf.c:167
#6 0x08048aec in wmf2x_draw (pdata=0xbffff8a0) at wmf2x.c:279
#7 0x08049518 in main (argc=1229353872, argv=0x49467390) at wmf2x.c:401

(gdb) up 1
#1 0x402d415f in free () from /lib/libc.so.6

(gdb) x/4x $ebp
0xbffff654: 0xbffff688 0x402c283b 0x08053258 0x00000000
^^^
chunk being free()'d

(gdb) x/30x 0x08053258-16
0x8053248: 0x41414141 0x41414141 0x41414141 0x41414141
^^^^^
chunk header

0x8053258: 0x00000000 0x40087000 0x40087000 0x40087000
0x8053268: 0x40087000 0x40087000 0x40087000 0x40087000
0x8053278: 0x40088000 0x00000000 0x00000000 0x00000000
0x8053288: 0x00000000 0x4038c440 0x00000006 0x00000000
0x8053298: 0x0804bb70 0x08000000 0x080532f0 0x00001018
0x80532a8: 0x00000000 0x0804bbe8 0x08053308 0xffffffff
0x80532b8: 0x0804bc30 0x0804bc40
(gdb)

++++++++++++++++++++++++++++++++++++++++++++

--
[ sean ]
[ pgp key id: 0x421C8CD9 ]
[ The advantage of a bad memory is that one enjoys several ]
[ times the same good things for the first time. ]

[ reply ]


 

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