zgv image viewing heap overflows

infamous41md_at_hotpop.com
Date: 10/26/04

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    Date: Mon, 25 Oct 2004 21:07:17 -0400
To: bugtraq <bugtraq@securityfocus.com>

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    Subject:

    zgv multiple heap overflows

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    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.

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    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)

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    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.

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    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.

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    -- 
-sean

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