From djb@cr.yp.to Wed Dec 15 14:20:33 2004
Date: 15 Dec 2004 08:14:16 -0000
From: D. J. Bernstein <djb@cr.yp.to>
To: securesoftware@list.cr.yp.to, alexcrow@users.sourceforge.net
Subject: [remote] [control] Convex 3D 0.8pre1 readObjectChunk overflows
    objectname buffer

Ariel Berkman, a student in my Fall 2004 UNIX Security Holes course, has
discovered a remotely exploitable security hole in Convex 3D. I'm
publishing this notice, but all the discovery credits should be assigned
to Berkman.

You are at risk if you take a 3DS file from an email message (or a web
page or any other source that could be controlled by an attacker) and
view it or convert it to another format using Convex 3D. (The Convex 3D
documentation does not tell users to avoid taking input from the
network.) Whoever provides the 3DS file then has complete control over
your account: he can read and modify your files, watch the programs
you're running, etc.

Proof of concept: On an x86 computer running FreeBSD 4.10, type

   wget http://aleron.dl.sourceforge.net/sourceforge/convex3d/convex3d-0.8pre1.tar.bz2
   bunzip2 < convex3d-0.8pre1.tar.bz2 | tar -xf -
   cd convex3d-0.8pre1
   env CXXFLAGS='-include /usr/include/g++/functional' ./configure \
   --with-opengl=no --with-x=no --with-gtkgui=no
   gmake

to download and compile the Convex 3D program, version 0.8pre1
(current). Then save the file 7.3ds attached to this message, and type

   convex-tool/convex-tool -i 7.3ds -o 3.obj

with the unauthorized result that a file named x is removed from the
current directory. (I tested this with a 1500-byte environment, as
reported by printenv | wc -c; this particular file 7.3ds is fairly
fragile, allowing only a 64-byte range of environment sizes.)

Here's the bug: In 3dsimp.cpp, readObjectChunk() calls readName() to
read any number of bytes into a 256-byte objectname buffer.

---D. J. Bernstein, Associate Professor, Department of Mathematics,
Statistics, and Computer Science, University of Illinois at Chicago

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