Security Insights

PHP Deobfuscation

PHP Deobfuscation

When I was analyzed the PHP scripts used for the "Hot Video" pages, I had to find a way to deobfuscate the PHP code. There are many tools and online services to obfuscate PHP, but very few to deobfuscate it.

Obfuscated PHP code: one big eval()

PHP obfuscation is generally done with:

  • Base64 encoding
  • Encoding strings into hexadecimal and octal values
  • Assigning functions to variables
  • Multiple calls to eval()


This code can be deobfuscated by hand, but it takes multiple iterations and can be time-consuming. Fortunately, Steffan Esser wrote evalhook to make deobfuscation easier. His article about the tool describes how it works. Basically, it is a library used with PHP to render code that is executed by the eval() function.

There are no instructions for compiling the source code, so it took me a little bit of time to understand all the necessary steps to use the code on CentOS5. Here are basic instructions to compile the code.

First, you need:


  • PHP >= v5.2
  • php-devel
  • PHP Zend Optimizer

CentOS5 comes with PHP 5.1, so you will need to obtain a newer version from another YUM repository. I used AtomicCorp to install the new PHP version and Zend.

Then, run these commands:



  tar xvfz evalhook-0.1.tar.gz  cd evalhook  phpize   ./configure  make  sudo make install

Now, you can use the evahlhook library to deobfuscate PHP files.


  $ php -d encoded_script.php

The only inconvenience I had to deal with when using evalhook, was that the resulting code still has strings encoded with hexadecimal and octal. So I wrote a small (and ugly!) Perl script to parse these strings into ASCII. Download if you're interested in using it.





  perl source.php target.php

-- Julien



Get the latest Zscaler blog updates in your inbox

Subscription confirmed. More of the latest from Zscaler, coming your way soon!

By submitting the form, you are agreeing to our privacy policy.