<!-- SBZ_reproduce  -->
Von: 		infamous41md@hotpop.com 
An: 		bugtraq <bugtraq@securityfocus.com> 
Betreff: 	zgv image viewing heap overflows 
Datum: 		Mon, 25 Oct 2004 21:07:17 -0400	 
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Subject: 
 
zgv multiple heap overflows 
 
++++++++++++++++++++++++++++++++++++++++++++ 
 
Product: 
 
zgv is a picture viewer with a thumbnail-based file selector, for the Linux 
and 
FreeBSD console (it uses svgalib). It's pretty featureful, and is probably the 
best svgalib-based viewer. (It can also be built to use SDL if you prefer.) 
Lots 
of people have told me they like it, where "lots" = "oh, it must be at least 
two 
or three", and you can't ask for a more ringing endorsement than that. Well, 
you 
could, but I'm not sure you'd get it. :-) 
 
zgv supports most popular formats, and allows panning and fit-to-screen 
methods 
of viewing, slideshows, scaling, gamma adjustment, etc.  
 
http://www.svgalib.org/rus/zgv/ 
 
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Vulnerable: 
 
I tested latest, zgv-5.5.orig. 
 
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Summary: 
 
zgv uses malloc() frequently to allocate memory for storing image data.  When 
calculating how much to allocate, user supplied data from image headers is 
multiplied and/or added without any checks for arithmetic overflows.  We can 
overflow numerous calculations, and cause small buffers to be allocated.  Then 
we can overflow the buffer, and eventually execute code.  There are a total of 
11 overflows that are exploitable to execute arbitrary code. 
 
++++++++++++++++++++++++++++++++++++++++++++ 
 
Details: 
 
01]readbmp.c:180:  if ((work_bmap = *bmap =  
                            calloc (w * (h + 2) * bytepp,1)) == NULL) 
 
02]readgif.c:498:  if((im->image=(byte *)malloc(width*height))==NULL) 
 
03]readgif.c:606:if((*theimageptr= 
                        (byte *)malloc(ginfo->width*ginfo->height))==NULL) 
 
04]readmrf.c:107:   (image=calloc(w64*h64*64*64,1))==NULL) 
 
05]readpcx.c:130:if((*bmap=malloc(w*(h+2)*bytepp))==NULL) 
 
06]readpng.c:225:theimage=(byte *)malloc(pixelsize*width*(height+2)); 
 
07]readpnm.c:147:if((*bmap=malloc(w*(h+2)*bytepp))==NULL) 
 
08]readprf.c:205:if((*bmap=work_bmap=malloc(width*(height+2)*planes))==NULL) 
 
09]readtiff.c:89:if((image=*bmap=work_bmap= 
                        malloc(numpix*sizeof(uint32)+width*3*2))==NULL) 
 
10]readxpm.c:183:if((colchars=malloc(ncols*sizeof(struct 
colchars_tag)))==NULL) 
 
11]readxpm.c:372:if((*bmap=malloc(w*(h+2)*bytepp))==NULL) 
 
++++++++++++++++++++++++++++++++++++++++++++ 
 
Exploits: 
 
There is a C file for each hole above.  The exploit for the first xpm hole, 
#10, demonstrates code execution,  the rest just crash zgv.  The only one I 
couldn't get working is the second gif hole, #3 from above.  That is in the 
file ximage_other_gif.c.  However, all are suitable for code execution with 
some work.  I just didn't have the time. 
 
++++++++++++++++++++++++++++++++++++++++++++ 
 
Note: 
 
There was also a hole in: 
 
01]readpcd.c:42:if((*bmap=malloc(w*(h+3-*output_type)*(*output_type)))==NULL) 
 
I couldn't find the PCD file format anywhere for free on the web, and didn't 
pursue this further.  I didn't see anything that would make it not exploitable 
though, so it looks valid to me. 
 
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Vendor: 
 
Was not contacted. 
 
++++++++++++++++++++++++++++++++++++++++++++ 
 
--  
-sean

Created attachment 25476 [details]
ximage_zgv.tar.gz

do not trust this exploit!

Looks like we do not ship this nice little tool anymore. 

dead! 

<!-- SBZ_reopen -->Reopened by thomas@suse.de at Fri Oct 29 08:37:45 2004

These bugs seem to affect xzgv too. 

Ouch, I'll take a look...

(should have clicked "Accept bug" also...)

Created attachment 25619 [details]
multiplication overflow check prototype

Okay, same problems exists in xzgv, indeed.

Hmm, would a check like this work? Checking every write access to the buffer
would be a PITA (especially for the implementation of the other image
formats...), but I'd like to have someone more familiar with ANSI C types and
bit operators to check whether this actually works on all of our platforms and
equally important, will continue to work with later GCC versions...

What does (size_t ~0) do? :) 
 
Assuming that all variables used are unsigned you can try the following check: 
#include <limits.h> 
... 
 
if(width > UINT_MAX / height) 
	EXIT 
if( (width * height) > UINT_MAX / 3) 
	EXIT 
 
malloc() 
 
 
 
 

And yes. width and height should be > 0 :) 

(size_t) ~0 does a bitwise inversion of a '0' of type size_t -- at least I hope
so... Thinking about it, it should rather be ~((size_t) 0). Since size_t is
unsigned by definition, you'll get the largest number available for size_t, as
size_t isn't necessarily "unsigned int" (size_t is defined as the largest
unsigned integer type available on the platform, if I'm not mistaken) and I
haven't found any SIZE_T_MAX #define... Is there anything wrong with this?

Created attachment 25749 [details]
Proposed fix for multiplication overflow

Okay, I think this patch should fix it. Can someone take a close look please
whether I've missed something? Would be embarrassing if we would issue an
update that does not fix the vulnerability...

 
looks good. thank you! :) 

Okay, submitted packages for 8.[12]-i386, 9.[012]-{i386,x86_64} and STABLE as
well as a patchinfo.

<!-- SBZ_reopen -->Reopened by thomas@suse.de at Mon Nov 15 09:56:39 2004

reopened for tracking by sec-team 

released updated packages on thursday...  

CAN-2004-0994 

CVE-2004-0994: CVSS v2 Base Score: 10.0 (AV:N/AC:L/Au:N/C:C/I:C/A:C)