Tag Archives: PHP/Agent.GC

How to remove malicious code infecting every PHP files of a website

A few month ago i stumbled upon some malicious replicating code (PHP.Anuna and PHP/Agent.GC) infecting all of my php files by inserting the same malicious code at the start of every files… slowing down all the website and gathering informations, this was a mess but it can be solved easily.

If you encounter malicious code from these or variants which are using the same signature i will show you how you can clean all of your website files very quickly and monitor it to prevent any other threats (look up the next article) so you can react before it is too late and let it to never happen again.

Here is a little PHP script to run on your server which recursively remove all the malicious code for every .php files in a specified folder based on a virus signature, it is very simple but also very effective for this kind of infection.

If there is any infections found it will show which file it cleaned up and where in the file the malicious code was, there is a report at the end of the decontamination process which will show you how much files were treated.

You likely have to configure it before using it because the signature will be different for each infections :

  • Change $target_directory value by the directory you want to clean up
  • Change $virus_begin_signature_str value by the few starting characters of the malicious code
  • Change $virus_end_signature_str value by the end of the malicious code

Disclaimer : I take no responsibility for any loss or damage suffered as a result of using this script, always backup your stuff first.

Note : Due to the use of the file_get_contents function, the script may get very memory hungry for large files.

$target_directory = '/var/www/';

//$virus_begin_signature_str = '$pmtccnmmns = \'341]88M4P8]37]278]225]241]334]';
$virus_begin_signature_str = 'd($n)-1);} @error_rP6]';
$virus_end_signature_str = '$pkvpncwqkl(""); $pkvpncwqkl=(468-347); $pmtccnmmns=$pkvpncwqkl-1; ?>';
$virus_name = 'PHP Agent.GC'; // just for pretty print, work with PHP.Anuna and variants

$recursive_directory_iter = new RecursiveDirectoryIterator($target_directory);
$iterator = new RecursiveIteratorIterator($recursive_directory_iter);

$decontaminated_files_count = 0;

foreach ($iterator as $filename => $cur)
	$path_info = pathinfo($filename);
	if (!isset($path_info['extension'])) {
    if ($path_info['extension'] !== 'php') {
	echo "Checking: '".$filename."'".PHP_EOL;
    $contents = file_get_contents($filename);
	$virus_begin_pos = strpos($contents, $virus_begin_signature_str);

    if ($virus_begin_pos !== false && $filename !== __FILE__) {
        echo $virus_name." found in '".$filename."'".PHP_EOL;
		$virus_end_str = $virus_end_signature_str;
		$virus_end_pos = strpos($contents, $virus_end_str) + strlen($virus_end_str);
		$before_virus_content = substr($contents, 0, $virus_begin_pos);
		$after_virus_content = substr($contents, $virus_end_pos);
		echo $virus_name." content between start pos ".$virus_begin_pos." and end pos ".$virus_end_pos." deleted".PHP_EOL;
		$contents = $before_virus_content.$after_virus_content;

        file_put_contents($filename, $contents);

echo $decontaminated_files_count." files were infected and decontaminated in the directory '".$target_directory."'".PHP_EOL;
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