From djb@cr.yp.to Wed Dec 15 14:22:56 2004
Date: 15 Dec 2004 08:29:07 -0000
From: D. J. Bernstein <djb@cr.yp.to>
To: securesoftware@list.cr.yp.to, o3read@siag.nu
Subject: [remote] [control] o3read 0.0.3 parse_html overflows t buffer

Wiktor Kopec, a student in my Fall 2004 UNIX Security Holes course, has
discovered a remotely exploitable security hole in o3read, a converter
for SXW files. I'm publishing this notice, but all the discovery credits
should be assigned to Kopec.

You are at risk if you take an SXW document from an email message (or a
web page or any other source that could be controlled by an attacker)
and feed it through o3read. (The o3read documentation does not tell
users to avoid taking input from the network.) Whoever provides that
document 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 ftp://siag.nu/pub/o3read/o3read-0.0.3.tar.gz
   gunzip < o3read-0.0.3.tar.gz | tar -xf -
   cd o3read-0.0.3
   make

to download and compile the o3read program, version 0.0.3 (current).
Then save the file 58.xml attached to this message, and type

   ./o3read < 58.xml

with the unauthorized result that a file named x is removed from the
current directory. (I tested this with a 535-byte environment, as
reported by printenv | wc -c.)

Here's the bug: In o3read.c, parse_html copies any number of bytes into
a 1024-byte t[] array.

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

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