What's new on phoneyc (3)--- Mid-term Evaluation

05 Jul 2009 Zhijie Chen gsoc libemu phoneyc shellcode spidermonkey

Mid-term Report on PHoneyC GSoC project 1

Introduction

PHoneyC is a low-interaction honeyclient written by Jose Nazario. The
shellcode (SC for short) and heapspray (HS for short) detection module
for PHoneyC is listed on the GSoC this year and I feel lucky to be
chosen to implement it. This report is the main idea about how to
detect SC/HS in PHoneyC and how to build and run this version of
PHoneyC. Note that this module (I call it honeyjs) is far from
complete currently and this report is only for midterm evaluation. So
it is possible that the way to build and run it won’t work in the
future.

As for the introduction to PHoneyC, I think I’d better quote what the
original developer said in his paper ‘PhoneyC: A Virtual client
Honeypot’:

This paper presents PhoneyC, a honeyclient tool that can
provide visibility into new and complex client-side attacks.
PhoneyC is a virtual honeyclient, meaning it is not a real
application but rather an emulated client. By using dynamic
analysis, PhoneyC is able to remove the obfuscation from many
malicious pages. Furthermore, PhoneyC emulates specific
vulnerabilities to pinpoint the attack vector. PhoneyC is a
modular framework that enables the study of malicious HTTP
pages and understands modern vulnerabilities and attacker
techniques.

My Approach

My approach to detection shellcode and heapspray can be simply
described as:

  1. Firstly I have modified the python-spidermonkey v0.0.1a
    (written in Pyrex) to let the Javascript Virtual Machine
    interrupted on each assignment.
  2. Then I check if the r-value of this assignment is a string.
    If so, I use libemu to check for shellcodes in this string. If
    there are shellcode within the string, it will append an alert
    message into the alert list.
  3. A series of shellcode alerts relating to one variable will
    be summarized into a potential heapspray alert.
  4. After the execution of the Javascripts, phoneyc will
    analyze the shellcodes for mal-download URLs and other
    information using libemu.

Also there are some optimizations such as mal-value hash table to
avoid duplicate check to the same value and dataflow tracking (e.g.
the concatenation of a mal-string (string that contains shellcodes)
with any other string will result in a mal-string).

The above is all I have done in the first half of this GSoC, and the
python module I implemented is named honeyjs.

How to Install

Requirements

To successfully compile the honeyjs module, the following
software/library is required:

Pyrex

“Pyrex - a Language for Writing Python Extension Modules.”
<http://www.cosc.canterbury.ac.nz/greg.ewing/python/Pyrex/>. I use version 0.9.8.5.

Spidermonkey(libjs)

“SpiderMonkey is the code-name for the Mozilla’s C
implementation of JavaScript.”
<http://www.mozilla.org/js/spidermonkey/>. I use version 1.8.0 pre-release 1.

Libemu

“libemu is a small library written in c offering basic x86
emulation and shellcode detection using GetPC heuristics.”
<http://libemu.carnivore.it/>. I use the version from the CVS.

Configuration

For the reason that I will rewrite the pyrex code in C to use the
latest version of python-spidermonkey, it’s meaningless to write any
automatic install scripts this moment. So you have to confirm the
packages above are correctly installed and manually change the path to
the libraries and header files in ./lib/setup,py and run the command
make to build it.

Run it!

To test this branch of PHoneyC, change the LINK variable in
honeyclient.py to your URL and run it. The shellcode/heapspray
alerts will be printed, the shellcode will be analyzed and the
URLs will be stored in a python list if it is a download-and-exec
shellcode.

NOTE: The deobfuscating module is developed by another GSoCer so the
current deobfuscating ability is limited. We will merge together at
the end of the GSoC.

For example, running the honeyclient.py on the test sample 2448.html
will prints like this:

## The outputs are all messed up in this blog, so I delete them. To view a complete version of this report, try http://joyan.appspot.com/2009/07/5/Whats_new_phoneyc_3_Mid-term_Evaluation.html  or the svn http://code.google.com/p/phoneyc/source/browse/phoneyc#phoneyc/branches/phoneyc-joyan-branch/doc/other/phoneyc_libemu_on_GSoC_mid-term_evaluation##

What to Do in the Future

There are some known problems with the current implementation, which
includes:

  1. The ‘strange’ behavior of libemu’s shellcode analyzing
    function. Sometimes the shellcode can’t be profiled thoroughly,
    for example, the download-and-exec shellcode in
    ssreader_0day.html sometimes can only finish the LoadLibrary
    and GetprocAddress calls in the emulation, and won’t go on to
    invoke GetSystemDirectory and URLDownloadToFile APIs, as seen
    from the shellcode profile.
  2. It costs too much time to check a heapspray sledge for
    shellcode. Some optimization is needed.

Things I will do next:

  1. Read the source code of the latest python-spidermonkey module
    (v0.0.8).
  2. Rewrite the whole honeyjs module in C. The current version of
    honeyjs is based on python-spidermonkey v0.0.1a, which is
    written in pyrex, but the latest version of python-spidermonkey
    (v0.0.8) is written in C and has less bugs. And also another
    PHoneyC GSoC project is also based on the latest version of
    python-spidermonkey, so it’s necessary for me to implement
    honeyjs based on python-spidermonkey 0.0.8, too.
  3. Write a more user-friendly install script for release.
  4. Document the implementation.
  5. Merge in Geng Wang’s DOM simulation codes.
  6. Try some new features, for example, hooking more APIs which
    will be called in the shellcode.

Following Milestones

July 12:

Finish Source Reading (Step 3).

July 26:

Finish the rewriting stuff (Step 4).

August 2:

Finish writing the install script and merging in Geng’s DOM
simulation codes. (Step 5 and 7).

August 10

Finish documentation and tests.