From djb@cr.yp.to Wed Dec 15 14:22:08 2004
Date: 15 Dec 2004 08:24:00 -0000
From: D. J. Bernstein <djb@cr.yp.to>
To: securesoftware@list.cr.yp.to, sshlien@users.sourceforge.net
Subject: [remote] [control] abc2midi 2004.12.04 event_text overflows msg
    buffer; event_specific overflows msg buffer

Limin Wang, a student in my Fall 2004 UNIX Security Holes course, has
discovered two remotely exploitable security holes in abc2midi. I'm
publishing this notice, but all the discovery credits should be assigned
to Wang.

You are at risk if you take an ABC file from an email message (or a web
page or any other source that could be controlled by an attacker) and
feed that file through abc2midi. Whoever provides the ABC file then has
complete control over your account: she can read and modify your files,
watch the programs you're running, etc.

The abc2midi documentation does not tell users to avoid taking input
from the network. Many web pages offer ABC files for public consumption.

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

   wget http://ifdo.pugmarks.com/%7Eseymour/runabc/abcMIDI-2004-12-04.zip
   unzip abcMIDI-2004-12-04.zip
   cd abcmidi
   gmake -f makefiles/unix.mak

to download and compile the abcmidi package, version 2004.12.04
(current). Then save the file 38-1.abc attached to this message, and
type

   ./abc2midi 38-1.abc

with the unauthorized result that a file named x is removed from the
current directory. The file 38-2.abc has the same effect but uses a
separate buffer overflow. (I tested these with a 426-byte environment,
as reported by printenv | wc -c; both files are sensitive to the
environment size.)

Here are the bugs: In store.c, event_text() has an unprotected sprintf
%s into a 200-byte buffer, and event_specific() has an unprotected
strcat() into a 200-byte buffer.

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

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