From djb@cr.yp.to Wed Dec 15 14:21:07 2004
Date: 15 Dec 2004 08:16:58 -0000
From: D. J. Bernstein <djb@cr.yp.to>
To: securesoftware@list.cr.yp.to, bhaak@gmx.net
Subject: [remote] [control] vilistextum 2.6.6 get_attr overflows temp buffer

Ariel Berkman, a student in my Fall 2004 UNIX Security Holes course, has
discovered a remotely exploitable security hole in vilistextum, an
HTML-to-text converter. I'm publishing this notice, but all the
discovery credits should be assigned to Berkman.

You are at risk if you take a web page (or any other source that could
be controlled by an attacker) and feed it through vilistextum. (The
vilistextum documentation does not tell users to avoid taking input from
the network.) Whoever provides that web page 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://umn.dl.sourceforge.net/sourceforge/vilistextum/vilistextum-2.6.6.tar.gz
   gunzip < vilistextum-2.6.6.tar.gz | tar -xf -
   cd vilistextum-2.6.6
   ./configure
   gmake

to download and compile the vilistextum program, version 2.6.6
(current). Then save the file 12.html attached to this message, and type

   src/vilistextum 12.html 12.txt

with the unauthorized result that a file named x is removed from the
current directory. (I tested this with a 540-byte environment, as
reported by printenv | wc -c.)

Here's the bug: In html.c, get_attr() reads any amount of data into a
32768-byte temp[] array.

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

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