++++++++++++++++++++++++++++++++++++++++++++ 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/ ++++++++++++++++++++++++++++++++++++++++++++ Vulnerable: I tested latest, zgv-5.5.orig. ++++++++++++++++++++++++++++++++++++++++++++ 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. ++++++++++++++++++++++++++++++++++++++++++++ Vendor: Was not contacted. ++++++++++++++++++++++++++++++++++++++++++++ -- -sean
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